The problem with air is that as soon as one side starts to consistently win the air battle, they get time to strafe ground targets and the other side gets zero time to punish ground. It snowballs from there. The side winning the air battle then also gets armor superiority, and from there the other team has no chance to win the ground battle. Yes, having superiority in one division should turn the tide of a battle. If one side has better infantry, they should have the upper hand in the ground battle. But air and armor can kill infantry as a counter. Similarly with armor, superior armor will help you kill more people and cap more flags. But infantry and air can kill armor. Barring stupid piloting, infantry and armor can not kill air the way DICE has designed BF3. All stingers and laser-guided things can do is make air kill you from farther away. In regards to air vs ground balance, I much preferred BFBC2's lack of jets. It just adds another powerful layer which is difficult and complicated to balance. Yes, highly skilled AA drivers and helicopter crews can kill jets, but generally speaking, the best counter for a skilled jet pilot, is another skilled jet pilot.
Under this assumption, for fun gameplay for everyone, the most important divisions to balance are the opposing air forces (and particularly jet pilots). The search for this air balance has put a lot pressure and restrictions on air players and leads to more scrutiny being applied to air as well as quicker and harsher enforcement of rules regarding air vehicles as soon as something questionable happens. I would answer that air vehicles add to the gameplay and make things interesting, but in the context of GC, the atmosphere that has been created as a result of trying to manufacture balance has resulted in my getting sick of hearing all issues air-related. Trying to manufacture balance has led to other things that I and others perceive as problems, but that's something for another discussion.