As stated many times before.
The game does not allow for a weeks-long suppression of enemy air defences campaign pre-game. (Only exception - AI buy of area/medium SAM for Iraq in the invasion since it's historically true).
The AI does not know about ammo trucks, so will not resupply any systems bought, unlike a human player. Nor will it move them about in a shell game like a human player al that much. So the human player will be able to "tease out" any existing ammo relatively easily or simply determine the launch area and splatter with arty before sending more air in. So the AI
requires a decent amount of ADA in order to give it a sporting chance against a human player. And that amount is easily dealt with by a thinking player (one recce strike to determine the area of launch, then apply arty).
But SP series games
start in ground artillery range. Therefore, there really is no requirement for fixed wing air whatsoever.
Tube and rocket artillery is the most cost-efficient way of delivering bangs on target. Fixed wing is therefore really only relevant for scenarios - where the designer can determine that the enemy ADA has been attrited by previous SEAD campaign etc., or human v human battles with some sort of agreement by the other side that sure, he wont buy any ADA and is happy to let your planes run riot...
Aircraft are therefore rather irrelevant in generated battles as and until the ADA assets are reduced - they cannot give any meaningful contribution until they (or others like say an SAS raid) have dealt with these. (Helos can at least use terrain masking etc to contribute to the land battle while staying out of the envelope of medium or larger SAM).
So in stand-alone battles, it is best really to spend arty points on tube and rocket batteries, since those are in range and tend not to get shot down. Arty is an all-weather asset as well (planes may not have night vision).
Fixed wing air in non scenario battles are really only useful if you have a total technological superiority of some sort between your aircraft and the enemy ADA. (e.g. fighting the VC or Taleban who usually only have AAAMG). Or against a PBEM opponent who totally forgot to buy any ADA whatsoever
!
Planes would be useful in a corps or division level map campaign, for their ability to be concentrated on a decisive point from airbases many miles away from the front. But this is not that sort of a map game. (And then you would still have to play an SEAD campaign before biffing targets most likely). The PROSIM games available from Shrapnel do that sort of thing I think ("operational" level).
Cheers
Andy