Less popular planes are just more attractive for some reason. Should the P40E see 20% of the usage in the MA, I'd probably switch to a different ride
And I suppose you're right Honch... in some cases it
isn't the challenge, and others it is. You can find a challenge in just about any aircraft. A challenge for me in an La7 would probably be 4v1. Should I be so lucky and I work my way down to a 2v1 or 1v1, it gets progressivly easier.
1v1 in non-identical aircraft always seems a heck of a lot easier than 1v1 in identical aircraft. Individual characteristics of each aircraft have both their exploits and their advantages. It's easier to morph a fight that way.
Identical aircraft 1v1 is usually boring scissors or a balanced turn fight, scraping your way into an advantage. If you lose, it's all on you.
With an early war ride, you'll win by flying your ride
that much more efficient and exploiting the other plane's weakness and the pilot's mistakes
that much more. Maybe it's an ego thing.
If I lose in a P40 vs. Yak9U, I can put some of the blame on the matchup

Convenient double standards

Most often in the MA when you find yourself in a P40 or F4F, 90% of your kills come from other pilots' mistakes.
In the end, landing 5 kills in a P40 versus landing 5 kills in a La7 is always more satisfying. Do more with less.