I think the air war was one of the flaws in DC1 and DC2 both. It's not just question of balance, but of the clunkiness of air superiority and air-to-air combat mechanics. Particularly maddening in DC2, where you have to guess where the Soviet air force happens to be based, with no effective recon or intelligence assets to assist. It quickly becomes random, repetitive and tiresome.
DC3 handles things much better with abstraction of the key elements of the air war... in DC3, I find the major flaw is an overstrong German AGS. IN the game, the Axis have ongoing use of two full Romanian armies which were in reality withdrawn from active operations after the fall of Odessa, and also have a number of far over-rated divisions (eg, 2 full divisions of Slovak troops rated as identical to regular German divisions!). As a result, it's relatively easy to do well as the Germans in the south, and the Russians have it really tough down there.
Otherwise DC3 is remarkably well balanced! I've won as Russians or Germans in PvP play, and I think I'm the only one who has beat the AI on the toughest difficulty setting. (OK, kinda beat. Took my designated objective of Leningrad and ended the game, but lost on points...)
I'll give DC2 another try, it's the one game in the series that I didn't play much of, due to frustrations with the air and naval systems and other balancing issues that felt wrong to me.