Since this thread seems to be filling up with comments and concerns, I'll add mine: unless I'm misunderstanding things, the AI air model is THISCLOSE to being broken out of the gate.
As aforementioned, AI-run air attacks are weighted to the first attacks launched, regardless of whether those attacks are against isolated and beaten up units. There's no easy way to avoid this-- either tweak the air doctrine settings every turn to stop attacks, or phase your high-priority attacks for the beginning of the turn. The former is click-cumbersome, the latter is less than ideal (like many players, I like to launch smaller attacks first, see what opportunities/breakthroughs develop, then send my mobile forces through. Sometimes the early attacks require the air support, but sometimes they don't).
Not sure what the solution is (I'm a consumer, not a programmer!

). Perhaps the kluge of a "launch no air attacks" on the main screen when launching your own attack, so you can tell the AI to skip that particular assault. Or, perhaps it's simply a matter of tweaking the weighting to be more proportional based on your reconnaissance, e.g. if your recon shows an 1 strength enemy unit is being attacked, then the AI will only allot a certain-size "strike package" proportional to that 1 strength enemy unit. Later on, when you strike a, say, 5 strength enemy unit in a 4 fort, the "strike package" goes up proportionally.
The trouble with the latter solution, of course, is 1) programming & math, and 2) you're either left with air support still eaten up by the earlier big attacks (a few large assaults and the airpower is eaten up for the turn), or left with air support unused at the end of the turn.
(Love the game, BTW... just discovering the inevitable quirks there are to discover).