I would complain that Engineers repairing critical damage to tanks and structures simply by burning them with welding torches and Pak-40's being wheeled around by two men ruined my immersion but this is just a video game so I suspend my disbelief and have fun with it. To each their own.
when i played with plastic toy soldiers as a 9 year old kid I didn't faction mix, its not fun its boring, it simply makes the subject matter of the game irrelevant, just because its a video game doesn't mean you should crap all over the contents of it in my opinion, the Allied - Axis side of the game I think is the most fun thing about it, you can use your imagination with all the stuff you mentioned, faction mixing sort of eliminates your ability to do that.