The fixed U/C fighters in question will need some nip & tuck in order to remain worthwhile. Adoption of retractble U/C is one of these steps. Eg. in Finland, such modified Fokker XXIs gained 'between 17 and 35 km/h' (
link), or 10-22 mph. If we can get 15 mph in average, that is a Ki-27 doing 292+15= 307 mph. Not bad when compared with 1st Ki-43s that were doing 310 mph. Less drag will also improve the range a bit (it was 1000+ miles with a drop tank per OTL on the Ki-27).
A5M was slower, partially due to it not having the closed cockpit. So we'd want to rectify that, while also making retractable U/C.
For the fighters with powerful engines - the Ki-44 with a bit bigger wing is my bet for the Army, while Mitsubishi might be doing a carrier-borne fighter around the Kasei, with folding wings and butterfly flaps instead the J2M.
Not having Nakajima making 3 different Army fighters in 1941-1944 in the same factory might get more fighters in total. Have Kawanishi also making the Mitsubishi's fighter under licence.