Firstly, those boat planes arn’t going to be good for balance or even be fun to play in game, and also I don’t want to include strategic bombers in the campaign because their payloads are too big to be fun for anyone. Secondly, the P-40 still gets stomped by the Zero as it is about as fast, but not nearly as maneuverable and would be a better match for the Ki-43. Also, I don’t get the hate towards the P-400 and the P-39, as both of those were very prominent during the early Solomon Islands campaign and would work perfectly in this game. Finally, the Buffalo and the A5M would be even worse for balance than the anything I proposed, with both getting completely stomped on by every plane with no chance of fighting back. The Ki-43 at least has a chance to beat the P-38 and the P-400 can reasonably fight against the Ki-44 or the Ki-61 if I decide to change them out, I’m still on the fence about that. The Buffalo and the A5M would not be able to do that in any way shape or form. Also, you have to keep in mind that these planes need to go into squads, and the squads need to make sense. A Marine squad can have an F4F and arguably a Corsair, but not a P-39 or a P-40 and vice versa for the army. The way you set up your proposals, there is no clean way to make the squads work well like that.
Top speed isn’t as important in this game as and the P-38 is a massive target. Sure the P-38 can accelerate and decelerate well and can outrun it, but the Zero can turn in on it and kill it that way. That is pretty much going to be the relationship between every US plane and Japanese plane, as that was the case IRL. Both sides have their strengths, and pilots must play to their side’s strengths to counter the other side’s.