This may be a one-off or a series for the blog, I haven't decided yet. The idea is pretty straightforward
"If we assume the entities involved have the same considerations as a real world nation and/or military, does a platform make sense?"
Part of the inspiration for this has been an interest I've had in the design and procurement process for different pieces of equipment for real world militiaries (exciting, I know), but this has also caused me to increasingly rethink how fictional military equipment is perceived and evaluated. To put it simply, both real world and fictional platforms have the same problem when people evaluate them. That is, the platform is viewed with the assumption that the end user's only consideration is having the best platform in the world (or galaxy in this case).
That is just not how the process ever works. There are countless considerations that lead to the development and deployment of platforms that would be generally considered sub-par. That being said, it is also rare that, given these considerations, a military will field something worse than what they could conceivably field. The disconnect is the myriad of unseen considerations.
Through that lens, let's look at the Venator and Imperial Star Destroyers and see if they would make sense if their operator nations were real-world militaries.
What is a Star Destroyer?
It's amusing that, even at this first juncture of trying to figure out what a Star Destroyer is, the Star Wars universe mirrors the real world. The term "Star Destroyer" is applied to a wide variety of ships of different sizes. Much like the question "what is a cruiser?" it seems to be more down to role within a fleet rather than a range of sizes or weaponry.
Star Destroyers are the backbone of a given fleet and produced in large numbers. They can operate alone or as part of a larger task force and can be called upon to conduct any combat task their operator navy may require. You may or may not have already seen one of the issues we'll be seeing throughout this breakdown. The Star Destroyer has so many roles within a fleet that it will simply have to make compromises in terms of what capabilities it focuses on. Compromises are always a thing on any platform, but the Star Destroyer's large mission profile is going to make these compromises more pronounced than usual.
Additionally, building ships and fleets is almost a generational undertaking given how long it takes to make even one ship. By the time you are in a full scale war, you may not have the luxury of simply making a generation of ships for that one conflict. The war will likely be over or the nature of the fighting my have even changed entirely by the time it sets sail to conduct combat operations. This means that most navies will have to simply make do with whatever they thought they would need a decade or more ago (see all the vessels from World War 1 or designed shortly thereafter still serving in World War 2).
Venator-Class Star Destroyer
Roughly a thousand years before the Venator ever plied the stars, the Ruusan Reformation dismantled the Republic fleet and demilitarized the Republic. This is significant because even naval yards being idle for 10-20 years can cause a significant loss of intellectual capital and experienced laborers. While some shipbuilding did take place for system defense fleets, it was in very scaled down numbers and prioritized features relevant to a peacetime environment. The mission profiles for peacetime and wartime navies are fairly different and don't necessarily overlap.
If we look at the Battle of Naboo, we see vessels we would expect from a thousand years of peacetime ship-building. The most capable ship was the Lucrehulk-class "Battleship" and I have to put quotes around the "Battleship" part. While the Lucrehulk was massive, it was also significantly undergunned for a ship of its size as it was just a converted freighter (more of a Q-Ship than a true warship). You'll also notice that, as the clone wars wears on, ships like the Lucrehulk become more support vessels as the core of fleets is increasingly comprised of dedicated warships.
We are going to have to come at this with an air of "Darth Sidious did it" because the naval buildup going into the clone wars is both improbable and problematic. It would involve a lot of resources over many years (see the current buildup of the Chinese Navy in the real world.) on both sides and if one side gets a substantial lead, the Clone Wars are basically over before they even start. With all of that out of the way, let's look at the Venator-class Star Destroyer.
The Venator heavily prioritizes its compliment of squadrons. It features massive dorsal launch bay doors that, when opened, allow for the quick launching and recovery of large numbers of fighters, bombers and transports in a short period of time. It also features prow, port and starboard doors to allow fighters to launch and land while leaving the ship less exposed. It carries Y-Wings for attacking ground and naval targets, ARC-170s for long range scouting and interdiction, V-Wings/V-19 Torrents/Z-95s for space superiority and even Jedi Starfighters of various models to lead strike packages or conduct special operations. The Venator could also use its large dorsal launch bay to conduct orbital assaults with LAATs deploying both clone troopers and their supporting equipment. A single Venator can conduct a wide array of simultaneous operations across a large area of space. Given how many of its squadrons were hyperspace-capable (and the hyperspace rings it carried for the non-hyperspace-capable platforms), the amount of space the Venator could project power over was incredibly large.
All is not rosy, however, for the Venator. The space dedicated toe fighters, bombers, transports, pilots, ordinance and clone troopers is not devoted to weapons and shields. The Venator is not as undergunned as the Lucrehulk, but does boast weaker weapon batteries than you would expect for a ship of its size and class. Throughout the Clone Wars, we see the Venator trade evenly in cannon exchanges with the much smaller Munificent-class frigates of the Separatist Navy.
Here, we see the lineage of the Venator on display. In a peacetime navy, small numbers of ships need to do a wide variety of tasks, many of which may not require their whole attention or effort. Significantly, a vessel in such a navy also doesn't necessarily need the best offensive or defensive systems as it likely won't face a peer adversary. More likely, it will be confronted with converted or ad-hoc vessels that will try to flee when they see an actual combat vessel. In that scenario, hyperspace-capable strike craft would be higher on the priority list than anti-ship weapons and defenses.
The critical problems with the Venator are two fold. First, all of its weapon systems are dorsally mounted as is the main launching and recovery bay. This means the Venator always has to make a choice between launching and recovering at maximum capacity or using its primary weapons. Second, the Republic Navy, due to a lack of options, is routinely forced to us the Venator as the primary vessel in its battle lines and, while in this role, the Venator cannot use its primary weapon system, its squadrons, effectively.
A lack of true ships of the line within the Republic Navy forces the Venator outside of its designed or ideal role and makes its drawbacks more pronounced. That being said, this is not atypical for real world navies. Simply waiting till an appropriate ship is launched from a shipyard or arrives from another theater is not exactly viable. Additionally, given the time involved to both design and launch a new ship (2-4 years depending on various factors), it would be fair to say that all navies go to war with what they have, not what they want and it will be up to captains and admirals to make the best of the vessels at their disposal.
So, why did the Republic Navy not design and produce a class of vessel to make up of the weakness of the Venator so that the Venator itself could serve in a more carrier-centric role in fleet actions? Remember, the Republic had no navy prior to the Clone Wars. They had to,not only stand up a brand new fleet that had an entire galaxy to exercise presence over, but also replace attrition losses. There is significant precedence in history of sticking with a design that basically works, even if it has issues, simply to avoid interruptions in production (see the US Sherman or Soviet T34 tanks in World War 2). The Venator, while not ideal for some roles, still worked as a ship.
Additionally, perhaps the Republic did start working on a significantly heavier-gunned and heavier-shielded design that had a reduced emphasis on squadron operations....
Imperial Star Destroyer
It's commonly said that militaries in general and navies in particular have a bad habit of fighting the last war. Part of this is because of the long development cycles of new platforms, especially in peacetime. This also arises because, when developing force structure plans, you have to just predict who the next enemy will be and how they will try to fight you. Even at the best of times, this is more art than science. Additionally, even if fleet planners identify what they need, the resources and political will have to be available to implement it.
Enter the new Empire in place of the Republic and a new fleet building concept around a vessel that is almost the polar opposite of the Venator. The Imperial-class star destroyer is a true ship of the line. It features considerable firepower and shielding, even for its massive size. Throughout the Galactic Civil War, the Rebel Alliance never fielded a vessel that could match an Imperial Star Destroyer in terms of firepower until the Starhawk-class at the very end of the conflict
But, you guessed it, tradeoffs. The Imperial-class features very limited squadrons and is top-heavy on fighters versus strike craft which indicates a purely defensive role for its squadrons. Not only are the squadrons predominantly fighters, but those fighters lack the ability to carry any air-to-ground ordinance and have limited range. Even the standard TIE Bomber has only a limited ability to operate in contested space being both slow and unshielded. This definitely indicates that they are merely there to protect or augment the Imperial-class rather than act independently as a combat arm. Additionally, this seems to influence the Empire's decisions regarding point defenses on the Imperial-class as, with multiple dedicated squadrons to protect it, the need of extensive point defenses should be reduced (in theory anyways). You'll also notice the primary launch and recovery bay, while smaller, is ventrally mounted which allows the Imperial-class to orient its weapons on a target without reducing its ability to launch or recover squadrons. The primary weapons system of this vessel is the turbolasers, not the squadrons.
This design makes sense for a navy coming out of the Clone Wars where pitched fleet engagements versus peer adversaries were routine. The priority is more on being able to take control of the orbital space around a planet and then maintain that control against a hostile navy so the world can be used by the Empire. In a battle in the Clone Wars, the enemy fleet has to be contested to use a planet. In the Galactic Civil War, the Rebel Alliance rarely tries to fight or maintain control of territory (and when they do, it predictably ends poorly). The objectives of the Rebel Alliance can often be achieved without ever fighting, much less defeating an orbiting star destroyer.
The main weakness of the Imperial-class could be best summarized as a lack of power projection. Despite having an entire legion of stormtroopers on board, the small launch bay and limited landing craft create a major bottleneck for deploying those troops in anything but the smallest numbers and limit the number and speed of squadrons that could be launched to protect/support that landing. In addition, the lack of hyperspace -capable ships or range in general on it's various squadrons limit their area of operations to the immediate space around the Imperial-class. Either the Imperial-class is in the vicinity and exercising power over that region or it's somewhere else and has no influence even if that "somewhere else" is merely in the same star system, a fairly short distance all things considered.
So, why doesn't the Empire start designing and building new ships to meet this new threat? Until the Battle of Yavin, the Rebel Alliance is a questionable threat to the Empire as a whole. The Glacatic Civil War is largely over at the Battle of Endor, a mere four years later. Even in the meantime, the bulk of the Rebel Alliance still suffers notable losses in both the mid rim offensive and the Battle of Hoth. Additionally, Imperial-class vessels aren't even present at the Battle of Yavin and most Imperial-class crews never saw a Rebel. Even at the Battle of Endor, only around 30 Imperial-class out of an estimated 30,000 are present and this is a force the entire Rebel Alliance fleet struggles to beat. The point here is that, the Rebel Alliance never posed a threat to the Imperial fleet as a while and could only achieve success through covert actions or eliminating Imperial leadership. Indeed, the Empire does start to push designs like the TIE Defender by the end of the Galactic Civil War that adds ordinance-carrying and hyperspace-capable squadrons to the Imperial Fleet. To put it simply, the problem isn't losing the Imperial-class, but rather that their enemy can win without fighting it.
Winning With What You Have
As we hit on earlier, navies go to battle with the fleet they have, not the one they want. We've looked at a pair of vessels that both have issues that hamper their performance in roles they commonly have to perform in their given conflict. So, why does the Venator-class routinely succeed even in battles where it should lose, and the Imperial-class fails in situations where it should be ideal?
The Battle of Scariff is probably the most telling. Two Imperial-class in orbit of Scariff are confronted with a moderate Rebel fleet. Between their own squadrons and the squadrons of the shield gate, the easy and correct strategy is to simply bring their turbolasers to bear with the TIE Fighters engaging the Rebels squadrons. We see when Darth Vader's Imperial-class arrives that the Rebel fleet isn't that considerable of an obstacle for the Imperial-class. Additionally, the Rebels cannot leave without the data, so they're trapped. This is an ideal engagement for the Imperial-class especially with their own squadrons augmented by the squadrons of the shield gate. Instead, the captains of the Imperial-class are timid to engage and the TIE Fighters leave their star destroyers completely exposed. There's a vexing lack of discipline and initiative on display. There is some historical precedence for this kind of, I guess, complacency in militaries that rarely confront peer adversaries whose capabilities they have to respect. The Imperial-class captains likely don't think the Rebels can win and don't feel engaging is worth the risk and the TIE pilots have likely never been in a battle where their Imperial-class is threatened.
If we contrast this with the naval engagement over Ryloth in the Clone Wars, we see the opposite. The Republic is confronted with a blockade and have to break through despite initial failure s of their primary weapon system, their squadrons. Both General Skywalker and Commander Tano formulate and execute plans using the limited resources at their disposal including using the relatively unimportant ventral section of the Veantor to absorb fire and close the distance for a fatal blow with their squadrons. These tactics represent a significant risk, but also show officers and crews that are both invested in success and willing to exercise their own initiative. The reason why the Battle of Ryloth is a great contrast point is that, early in the battle, Commander Tano make a poor call , resulting in a heavy loss for the Republic. Sometimes risky strategies are required even though they don't always work. The Empire routinely suffers embarrassing losses that could be prevented by their officers taking any initiative.
The Imperial-class is remembered poorly and the Venator-class fondly because of their crews.
Conclusion
I doubt any of this is intentional by the various entities that curate Star Wars content, but, looking at real-world parallels both of the deisngs made an increasing amount of sense. You could say "why build the Imperial-class?" but why build the Yamato or Bismark either? It's easy to look back and say carriers are clearly the right way, but the officers planning fleets out in the 1920's and 1930's had no way of knowing the flimsy biplanes of the time would evolve into capable weapns in their own right. Every ship, tank, rifle, etc is a series of compromises and, at the time, those compromises will usually make sense even if they end up not being worth it later.