I’ll post here since it’s in a similar vein as something I was going to post as a suggestion. Also because what your proposing is exactly part of the issue we have still - it’s just merging a tech tree and all. And you write off battleships too fast - especially if you look at the various ships in game as is even beyond BB’s, at higher BR’s against modern aircraft and/or more modern missile ships. Because the last BB’s were retired in the 90’s, and they had had a bunch of modern upgrades by then. Your talking heavy metal behemoth’s that had at least 4 PHALANX turrets to shoot down missiles or aircraft, fixed positions of Stinger missile launchers, and launchers for RGM-84 Harpoon missiles. So given the current 70-80’s frames of the max tier aircraft (maybe even later) - they have options to be well equipped against any modern ship or plane of the time.
I do think Bluewater and Coastal should stay separated, someone wants to run PT boats against Bluewater - their choice to have fun with that. Plus they should have the options to complete events/missions in them - especially after the condensing of trees really screwed some things up taking certain planes down in rank (like the F6F hellcat that can’t complete things anymore).
I hate to say it, but the other game I left in this regard had the right idea - the various base types, Destroyer, Cruiser, and Battleship, really need their own trees. I’m sorry - Arizona has no business at 7.0 when it has at best maybe the refit right before she was sunk that wasn’t even enough for planes of it’s time, let alone 7.0 where it’s mostly jets, maybe high end props with insane payloads like the AD’s. Meanwhile opposite side their adding Roanoke where the highest actual cruiser is 6.0 which not only was this thing more jet age as it was, but will pretty much shred anything that has to fight it on it’s BR, let alone a lower BR plane if someone gets the short straw and their BR 5-ish lineup has to fight it. As is theres a ton of weirdness with more modern ships or more modern refits of them then to an older ship/refit with worse capabilities in fields - the most over the place being AA ability. The 1944-45 builds of Sumner/Gearing class ships are slightly behind in BR to Sommer and Porter Destroyer Leaders that have some .50 cal’s and a couple ‘Chicago Pianos’, and I believe have been mistakenly given AA ability with their main guns when those two classes specifically use a single purpose mount, unlike the Gearing/Sumner/others - at least until those two classes were given various modifications that reduced the number of guns and had varying numbers on how many were DP guns, and they aren’t the ones in game.
While there are some, like Mitscher, that are weird to place (the 2 gun armament is still pretty light, no heavier anti-ship weapons unless they change to the DDG conversion) the BR range should probably extend from around 3.0 to 8.0 (least in Arcade) with a current DD line starting with lets say Litch at 3, Aylwin at 3.3, the as is Porter/Somers classes at lets say 4 and 4.3 respectively (with the errant DP ability removed), Fletcher stays as is, with Sumner and Gearing bumping up to 5.0, maybe 5.3 (not 100% sure those versions should go much higher than that, though are argument can be made to put them closer to 6.0), but it gets kinda weird post war till you get to DDG’s because while yeah Mits has better penning rounds and RoF - 2 guns, no actual anti-ship torpedoes, still pretty limited AA ability is hard to put against some of the tougher cruisers/BB’s. Even if both lines start with Light Cruisers, there should be a light Cruiser line (that would end at Roanoke at 8.0 when added) and Heavy Cruisers line (likely ending with Alaska at 8.0) that can spread out through the BR’s with things like Trenton as a good baseline starter - though not sure if it should be 3.0 or maybe start a little higher. Battleships - me personally, I’d start the Dreadnought type/era BB’s at 3.0 - they’re mostly vulnerable to air attacks, big and slow, long reloads, not the most accurate guns - yeah tons of armour so my DD’s I’m relying on torpedoes or setting something on fire as I annoy it with basically peashooters, CL might get some pens depending besides relying on torps, but I’m okay with that. Especially since it also means more a reason to use the AP bombs they added on lower BR planes. Though at least on the US list, not sure I’d put any past 6.0 of those in game yet cause yeah, tons of AA but these are still more Dreagnought era or just after that got mainly AA upgrades, maybe some better fire control and all. Wouldn’t really put anything in the over 6 range till really eithers the late war refits of something like NC came in to the game, or later refits of the South Dakota’s, with the as built Iowa’s absolutely at the top end where they see Korea-era aircraft/jets with how much lead they can throw in the air and everything. With anything past 8.0 being one of the later refits of the Iowa’s where they also have more modern weapons/defenses to deal with more modern aircraft/warships/weapons.
But, that’s me, I’d rather see a mix of ships at the ranks/BR’s that are more appropriate to the ships time - be that as built or it’s refit/rebuild, where they aren’t bullied by way more advanced aircraft than they should be (a lot of the BB’s), or bully the aircraft that are that much older by comparison (several CL’s and even some DD’s) with more lead and shrapnel than the slower planes can hope to dodge, where you have DD’s/CL/CA/BB of an era interacting in the same battle, and having to know your types strengths and weaknesses vs others.