I just think that this game has evolved from a flight simulator to a World War 2 simulator
While it's no longer a 'pure' flight combat sim, it is absolutely not a WW2 simulator in any way. It's just using WW2 equipment for a fantasy setting (at least in the Mains), and for a very good reason.
Just think about the gameplay balance. How popular would the Rook side of your example be, when all they got are German and Italian equipment? Just think of B-17, B-24, B-26, B-29, Lancaster vs Ju-88 and Arado 234...