The US airforce would've been great as the Soviet airforce. RAF would've also been more than just fine.The Soviet Air Force was, by the latter part of the war, good at being the Soviet Air Force. Rubbish at being the Royal Air Force or the US air force as they were at being the Soviet Air Force. The test has to be if it was fit for purpose. It's purpose not other air force's purposes.
We can recall that the best aircraft the Soviets had were with Western genes.
The Soviet AF would've been a bad replacement for both the RAF and for the USAAF.