The F4F actually was involved in the Aleutians and did shoot down enemy planes. There numbers were limited .. somewhere around 12 or so. The Aleutians theater had a hodge podge of aircraft.
Now as to why the Ki61, yes it historically was not there. However, for game balance reasons it has been included. Basically the Japanese had plans to expand their operations in the Aleutians and start working up the chain but these were abandoned a few months after Midway.
Also realize that we actually have more players involved than there were planes involved in the real campaign.
So the Aleutians to some extent is a what if event modelled on the historical campaign. The what if parts are what if the U.S. and Japanese poured more resouces into the event and contested it more than we did. Also the U.S. did have quite a few P38Gs active in the theater. As a designer I wanted to have some involved to give the flavor of that but the A6M2 is no real match for the P38G. So as a designer to balance things for game play I decided to only have a few P38Gs active (12) and then my logic is if the Japanese were really contesting the area and hoping to use it as a base for invading North America (it was a concern at the time), then it is logical to assume they could have put some of their more advance fighters into action there. In this case I am letting the Japanese have 12 (Ki61s).
As for the other planes .. Betties were active (so have the Ju88s subbing). F4Fs were active but withdrawn in the phase after Attu and Kiska failed and before the U.S. retook them. They were actually shipped off to the S.W. Pacific because they needed the F4Fs. P39Ds were actually withdrawn before the U.S. taking back Attu and Kiska mainly do to their tricycle landing gear not holding up well in the brutal Aleutian environment and their short range. With the bad weather conditions up there (which kept the fighting low to mid alt) getting lost in the fog was deadly, especially if low fuel.
B25s were active as was the A20, B26, B24 (not using because of game / design decisions).
