Late game air is not decided by peak APM, creating tight ASF groups is quite easy if you practice it a bit. Late game air just requires you to react immediatly when somebody is trying to snipe your teammates, that is different from APM. Rest of the time you just participate in game enders while adding air factories to your grid.
Correct current late game air is not dictated by apm, it's numbers + micro. Someone with a below average apm could beat an apm god on air micro with how it is now. I'm talking about your suggestion where it ends up being a who can spread out their air best micro. That's highly apm intensive and very tedious micro.
The issue with asf is that you can go into a fight with 200 asf vs 190 asf, both be even in micro skill, and then the guy with 200 somehow ends the fight with 150 left and the other guy 0.
Dont think this is true, if both players manage to get somewhat behind each others ASFs they will loose units at a somewhat equal rate. What you describe only happens because ASF react with a lot of delay, so it is kind of hard to control their behaviour, but not impossible. Therefore its easy for one of the players to fuck it up.
I play entirely too much mid to high level Seton's. While it doesn't happen all the time it happens very often. It's rare when you end a fight with both players having roughly the same amount left over at the end or one player has say 10 out of 200 left at the end. I'm not talking about fights where you're microing the units, I'm talking about fights that are large enough where the correct micro is to just hit stop when they engage.
The point of the AoE changes is that you should have to make a strategic decision which kind of air to produce based on game situation, instead of just competing for creating the bigger ASF cloud than your opponent. Micro is of course going to be possible and important, just like it is important in land and even somewhat navy.
What this will do in practice is cause a new air meta where you mix in ADF with your asf and then have a micro war to see who can snipe the others ADF faster and then win with ASF. Because Air Superiority Fighters are just that, meant to get air superiority. Their use is analogous to fighter planes in WW2 for instance. A unit to counter them by definition just becomes the new ASF.
About overkill of SAMs:
Currently SAMS kill way less ASF then they should be if we go purely by DPS numbers. This is fine because SAMs are balanced with this in mind, but they don't do close to full DPS to a ASD cloud that moves by, because they shoot way too many missiles at the same target, and missiles are quire slow, so when the target dies there are already a bunch of missiles in the air that are gonna loose the dead target and be useless.
By giving ADF more value per unit, you would reduce overkill percentage, because SAMs need to switch target less often.
Fair point but doesn't really change anything. If people hate asf blobs this much have you tried making some mobile flaks? You know, the unit already in the game and already designed to kill groups of air units or slow moving targets? Mobile flak wrecks mismanaged ASF blobs. Static flak too.
All this is doing in my opinion is recreating the original problem, but now with more steps.