That makes sense.
But Ki-43 is essentially of same level with Zero, perform pretty alike Zero, rather than a reasonable upgrade as the time frame suggests.
However if I were you, I'd make both navy fighter and army fighter buildale in each time frame, and give the navy fighter some specially advantage over sea but also make it more costy.
Perhaps let the carriers to offer a bonus to navy fighters, as Thor Gunship does in MO 3.0? I think that would be interesting, if carriers can swith modes between support figters and launch attackers, and it take some time to swith, then you get the possibility of Midway: Caught by your enemy while swithing modes!