The only weapon aircraft truly fear are Gauss rifles, which are carried by only a handful of units - and the ones that are on mechs don't count. Even the Demolisher has to be propped up on a hill to engage air units. The only actual *unit* that you're complaining about is the Harasser, which has less armor than even the Shiva does, and it's only good at anti-air and some anti-BA. Even a clever pilot can Wild Weasel one-shot the Harasser. Everybody on the ground instantly targets the Harassers because you just bump into them to cause them to explode spectacularly.
You might have a point if everyone on the ground was able to dump all kinds of firepower into aircraft, but as it is that's not the case at all. I might even agree with you if LRMs could consistently hit ANYTHING in the air that did more than even a basic maneuver. Again, not the case.
Essentially what you're asking for is for ASFs to be immune to the only real hard counter that ground forces have to deal with them. You want to be able to get hit by a Light Gauss in your little plane that costs next to nothing but carries two missiles capable of causing catastrophic damage to ANYTHING on the ground, and get a 'second chance', for you to go 'oh my, I'm getting hit! This is upsetting!' and slowly cruise away to safety, exactly like how VTOLs react to UAC2/5 fire, exactly how all aircraft react to missile fire. If I had my way, aircraft would simulate reality - if you wander anywhere within range of an anti-aircraft unit, you supernova in mid-flight and die so hard it kills you the next four times you try to respawn.
Yeah, sure, good thing I don't have my way, right? No, because realistically? I'd delete aircraft completely. Just band-box the hangars in every map, press the big 'ol 'DELETE' key, and remove these insipid fapping things from the game completely. I don't know what purpose they're supposed to serve, but the only thing I can gather is that they are there so that Cowboy Roy and his buddy Maverick can vacuum up easy points. ASFs and VTOLs are, without a doubt, the 'sniper' class of MWLL. Every FPS game has this - a category of weaponry or class of player or what-have-you that exists solely to allow one player to have fun and rambo and completely ignore his team and the objectives, and to get easy kills with almost no threat to themselves.
Why do you think people like Marshes so much? Half the reason is because there's no god damn aircraft. Why do you think of the four custom maps we have, there's not a single airfield on ANY of them? Because these damn things serve absolutely no purpose in the game, all they do is frustrate EVERYONE except the one guy running laps between the battlefield, the airfield, and the edge of space.
A not-insignificant amount of people have quit this game because of their frustration with LRM boating and aircraft. I've never even HEARD of someone disliking Marshes or Inferno because "they don't have enough aircraft". I'd happily trade the couple of losers who would cry in their tea and quit the game forever without their precious aircraft if even just for the CHANCE to bring back the ground-pounders that quit this game in sheer irritation because of them.