I agree with pongo.
Had the germans been knocking on the door to chicago in 1945, while the Japanese were driving on Dallas, I would expect that the P-51H, F8F and F7F would have fired some shots in anger while the TA-152 would not.
The only significant difference is that the Allies had the luxury to slowly and safely train up fully operational squadrons in the rear specifically to fly the new types, and when they were ready move them to the front. Even the Meteor, which was ready to fly front line combat fairly early on, was held back because there was no need to rush it to the front.
The Germans and Japanese lacked the fuel to do the same training approach, and even the ability to train up in safety. Kurt Tank's story about outrunning the Mustangs tells it all. Do you think the head of FW would have flown in a combat zone if it weren't for the fact that all of Germany was a combat zone? Why not rush initial production "trials" aircraft directly to the front lines? At least the "veterans" in 1945 had a few hours of flight under their belts -- better than loosing them on the ground or to the Russians.
IMO you can go either way from a fairness standpoint. Include inital production series aircraft like the Ta-152 where a handful were thrown into the meat grinder before their time because it just didn't matter, and include the aircraft that were at a similar production/deployment stage but not pushed directly to the front line because there was no need. Or, don't include either.
Personally, as GSholz points out the MA is not meant to be a recreation of WW2 so for me, the more the merrier. Might even be some planes actually worthy of the typically hight perk rates we see.
Charon