When they spawn on the ground, they need to climb to get a good approach angle. Flying low isn’t very effective with guided weapons. An experienced player will always dive upon spawning if an AA is detected. If no AA is detected on the RWR, they can immediately fire their AGMs at tanks from above.
Forcing a ground spawn would make players take longer to side-climb before using guided weapons. They would have lower speed, making them easier to detect and shoot down.
Also the ATGMs wouldn’t benefit from the speed and position of current airspawns. Right now a Suchoi spawns with almost mach1 already at height with perfect view onto the battlefield.
The other way araound is also not really fair tbh. I often have players spawning an SPAA faster than I could retreat my plane or heli. Means you kill a tank player and like few secs later he’s in a missile SPAA shooting you down :) Quite arcadey. A couple of years back there was a spawn delay of 20 sec or something. Now you can spawn immeadetly to retaliate air to ground or ground to air.
Considering the rewards for playing AA i think not having spawn delay is more than fair. You get no rewards for sitting in an AA waiting all game so you should be able to spawn immediately in an AA to retaliate against CAS. Especially when CAS is so potent. Its more than easy enough to dodge someone spawning AA after doing a CAS run