I believe that the AI is bad enough that you could rush bb3 and still beat them.
When it comes to MP, the meta is something that is going to suit the environment, either the ruleset, or whatever gentleman's agreements are being made. As an example, I like to look at the battletech universe, where giant expensive mechs are the main weapons of war not because they are particular good weapons, but because the mechs had a single pilot. They were treated as an extension of the pilot, an individual. The mechs became more about status and personal glory, they became the 'meta' choice because there was an environment that supported their use, even in the face of superior weapons like tanks.
Which is a long way to say that if you're doing MP, you could have some sort of ruleset or agreement to just... RP, like you intended.
I think this is more or less the crux of my concerns here. Did things get 'better' through the generations of pre/post treaty/war, or did they simply get bigger. Getting bigger isn't really what I would consider to be an advancement in hull design, it seems more like brute forcing like the yamato. If anything, I would say that restrictions like the treaty limits on size/guns would specifically motivate designers to find ways to get more out of what they're allowed to have and come up with, a 'better' design.
I'd say we're still well within the realm of the topic, that topic being more of the specifics of the designs of the battleships.
Of the 6 naval powers (USA, JAP, ENG, FRA, GER, ITA), only 4 of them even planned for a battleship outside of the mid 30's (ENG, USA, FRA, GER), only 3 of them would be a '39 design (USA, ENG, GER), and one of those wasn't really a 'complete' '39 design because the guns weren't ready and the plan got kicked along and slowly morphed into a '41 design (ENG). So that is 2 navies (USA, GER) out of 6 that seemed to actually have a workable design in '39. Which is more than the 1 navy that had a '40 design (FRA) or the other 1 navy that had a '41 design (ENG), but most ways you cut it that's only half the navies that this 3 year cycle seems to match, and I wouldn't call that most. Trying to take the average of 39/39/40/41, we get 39.75, which is closer to 40 than it is 39. That counts on discounting the lion though, which you disagree with.