Lastly, I don't think it's the airframes themselves that are the problem. I think it is the slow pace of air ops prior to you taking the game.
I humbly suggest there is one other factor: CR has taken the "Northern Route", which has its advantages, but doesn't interfere with Japan's access to the Southern Resorce Area. Given that in this scenario, Japanese ASW is more effective, and the USN submarine arm correspondingly less so, I would expect that the Japanese economy is turning out fighters (and other war material) at a much greater rate than is typical.