Also this from Scarper, one of the devs (Old Forum, 11 Aug 2016, quoting at length because old forum could go away soon):
Spoiler
Several reasons why we are focusing on the “smaller” fleet.
1.How to play?
It is clear that game play for very big ships is different from game play in tanks or aircraft. Such a huge and unwieldy ship must have an appropriate battlefield and adapted mechanics. Cruisers can easily battle against other cruisers, what will make a head to head battle until the first hit, where the hit ship will just die slowly without any chance to strike back. No health points, no instant repair, only big ship which slowly sinks to the bottom and a player that can only watch while his ship is destroyed.
This game play will bring a dubious pleasure, but it is realistic, because large ships are destroyed in this way. What about action in the locations, they need to be equal to fighting units - the players need time to re-group the ships and prepare for battle. But with dozens of minutes convergence alone, during which everything could end even before it begun - some wild hit from a distant gun, without aimed fire as there is no line of sight, yet the defeat is already quite real, and it’s over.
As for interaction with other types of vehicles, here-in lies some further difficulties. In locations that are suitable for the interaction of different types of vehicles, these ships don’t just rotate on the spot so they are unusually vulnerable just to small torpedo boats. At the same time we can not afford to change the characteristics of these ships, we can not increase their speed and agility, as then it will be required of the lighter vehicles also. What is the outcome of these changes? Totally unrealistic battles, to the extent that a generic bomber will simply not be able to catch the ship, such a boost would be needed to the characteristics of the ship to allow it, for example “a cruiser” to have slim chance in escaping from under the enemy shots.
The main issue is, Assume that the average time of battle in WT will be about average time of battle in real life but with a wee bit subtracted because our players dont want to keep their vehicles in one piece. You can think of the Battle time of “each” vehicle from the first shot fired, or the time that the enemy was sighted - This is also true for air battles, it is true for tank battle and it will be true for naval battles IF we are determined to keep the physics and damage model reasonably close to realistic. So, at sea, with higher tonnage, the truth is that the average battle is MUCH longer than an hour, even for 1-2 vs 1-2 ships. whilst in real life, it never was shorter than 20 minutes - so it will be in WT. When 20 minutes is longer than average battle in any mode, it is still OK for Naval Forces, But an average of 2-3 hours for a battle is generally more than average player will subscribe to. We made it and we played it - but you do not have to trust us. Just use common sense - realistic physics with reasonable scenarios will cause realistic battle duration’s (or maybe a bit quicker, but this is only about a players interest in getting to the action quicker, taking risks, not something else)
Aircraft, tanks, bang - whack, bang - whack caboom, Ships, bang, …bang…bang…(silence) splash splash, splash (incoming) etc etc, it isn’t the same, not by any stretch of the imagination. I see Battle of Britain used as an example of a long air battle, it wasn’t a single engagement, battle of the bulge - again wasn’t a single engagement - aircraft, tanks, SMALL ships - short lifespan in terms of single combat in our game, large, heavily armoured capital ships, long lifespan in single engagements (unless you are really lucky like in rl) Nope at this stage it just doesn’t make sense.
2.Mechanics
Even small motor gunboats could have a crew of more than 30 men and this is not a small number, with our “craving” for realism large ships will not fit into the dynamics of game battles. Even huge vessels are extremely vulnerable to aircraft and they had very complex tactics, including reconnaissance, protection, long range combat and even rules to their movement do not comply with the gameplay - fighting for frags and rewards.
Capital ships move so slow that they cannot dodge ANY hits at the distance they are fighting at. The only possible solutions are either boost their speed x5 at least so they can dodge or limit the shooting distance. But even if we boost the speed x5 (making it equal to the slowest aircraft) that won’t solve the problem of shooting beyond visible range.but still it is possible that one ship can destroy another with a lucky shot - e.g.Bismarck vs. Hood. Two shots fired, battle lasted 30 minutes, hood sank in 3
Maps could be made bigger but that would involve hours and hours of travelling only to get taken out in the first few minutes of contact, there are a few of us who would be happy to do that, but there are just too many that wouldn’t.
3.Economy
Ships DO take longer to sink, even one lucky shot can take a whole ship out of action, without destroying or damaging critical modules. Even with critical damage it would take hours for a capital ship to sink. Thus without simplifying damage model to a HP system or the like there will be no game play at all
How can you count kills?
In reality destroying one capital ship could take hours and hours, and, sometimes seconds - in case of ammunition explosion. With smaller vehicles it is clear - destroying an enemy brings greater rewards, damaging an enemy also brings rewards or can take several hits to destroy an enemy. With ships that have crews of over 1000 men for example, it is much more complex. It is exactly the same for the economy and research and development - even if we ignore big crews with a great variety of functions and qualifications and hundreds of different modules, there is still the question “how many millions of “lions” should a torpedo bomber receive that has taken down a capital ship with a lucky strike?
For such battles we would require a significantly redesigned game mechanic - a completely different gameplay.
4 Imbalance in Nations
As we know, and let’s be honest about this, not all nations had a heavy warship fleet that could match the opponents at the time. There would be nothing up front that could appear in the development of the tree and compete on equal terms with their opponents unless we use small ships to begin with.
We aim not only to give you the very existence of warships in War Thunder, but also to create highly interesting gameplay as well, which would fit into the overall concept of the game, allow each player the participation of all types of equipment in a single battle. The US, Great Britain and Japan had indisputable superiority over the USSR in the number of aircraft carriers, which immediately deprives the USSR of this class of vehicle from the beginning - and yet it happened not because of the technical backwardness of the Soviet Union, but for the simple reason: the Soviet Union had not experienced a great need for these ships, because the main fighting took place both on land and in the air. The same can be said for Germany, their naval power was not the greatest at the beginning of our time frame. But how do we explain that to the many players across the world who still want to be the best? Make no mistake, many players use the soviet and German nations in game.
At the same time, small class ships were common to all nations, and here they are just perfect for most of the current vehicles represented in War Thunder lines of development.
5.Specialty
One more issue is that vessels such as battleships were used very selectively, battles lasted for hours and even days and often ended with an enemy retreat or not being destroyed. Moreover ships such as the “Yamato” or “Missouri” were unique in their class, and definitely, players wouldn’t like to wait in the queue because the single e.g. “Yamato” for the current battle has already been taken, or dozen of battleships in one battle without a supporting fleet will be a clumsy and easy target for aircraft.
Some of the admin comments to that thread were awesome sauce too, looking back: Smin1080pYT for instance saying “The point being you could not [realistically] have 16 Yamatos”… also “But by making the “perfect” all round situation for a direct confrontation of ships that would result in, a say 30 minute battle, you effectively have cut every aspect of a true unpredictably real battle out and cut and gutted the complexity of naval combat down to a 16 vs 16 arena arcade game. Other games have done that and we are not out to do the same.”
Also: " The “perfect situation” you were talking about for [capital] ships to result in an under 30 minute match would require both teams to have almost identical composition and be placed so specifically that almost every battle would be identical and play out the exact same way.
“You would remove all sense of tactical and strategic thought and severely simplify the complex nature of Naval Warfare… It removes all of the tactical, strategic and complex value out of naval battles” (And yet, 9 years later here we are.)
To the point at hand, the official answer from the linked Q&A was: “Player-controlled destroyers and other large ships may appear later, in other gamemodes, it will be decided based on results of closed beta.”