Humble, it depends on how you look at it. You are focusing on numbers built, which is valid in one way. I, and I suspect Helm, look also at the variety of types build. Japan fielded a very large number of combat types while not having the industrial base to produce them in the tens of thousands, often not even in the thousands. But they did have a very large variety of combat aircraft types, second only to the USA. And more types means more flavor to the game, and that is another valid way of looking at it.
Too my mind the Japanese and Russian sets need the most attention. Then the Italians. The British and Germans still have some significant holes too.
Here is a list of Japanese aircraft that would not be horrible in the MA:
A6M3a (a halfway mark between the A6Ms we have)
B6N (mid war carrier strike plane, more than 1200 built)
B7A1 (late war carrier strike plane, never operated from carriers, more than 100 built)
D4Y (very fast carrier strike plane, more than 2000 built)
J2M3a (fast climbing interceptor, about 500 built)
Ki-44 (mid war fighter armed with four 12.7mm guns, more than 1200 built)
Ki-46 (recon and heavy fighter, more than 1700 built)
Ki-102 (late war strike aircraft and heavy fighter, more than 200 built)
N1K1-J (earlier version of the N1K2-J, less ammo, almost 1000 built)
P1Y1 (Fast medium bomber, more than 1000 built)