Fairness between game modes, actually making the game playable for history/vehicle enthusiasts who have a favourite vehicle or group of vehicles and letting them focus on it.
I like my corsairs. If I want to fly my corsairs, I don’t want to bother with tanks. I can do that and have fun.
I think the F2H-2 looks cool. I can take it out and fly it without regard for tanks (absurd spawn costs and zomber-infested brackets not withstanding).
I like my demon, it’s not a plane I’m as passionate for as WW2 pacific theatre things, but it’s pretty cool and still a carrier aircraft.
Regardless of what tank I like, I cannot use that tank without being punished for not wanting to fly that day. Not interwar. Not WW2. Not cold war.
I can’t even play GSB over GRB because “Sorry, your chosen vehicle is not in rotation today”, so cannot even fall back to “well, at least the planes handle in an intrinsically fun way” when forced to use them.
I’m pretty confident in saying I’m decently competent with my planes and flying them in GRB is an exercise in torture due to the later listed reasons. The lack of markers is nice. The other things? Not so much.
A not insignificant amount of pre-missile aircraft prefer combat at altitudes far exceeding relevant altitudes for GRB and prefer trajectories that a tiny 10x10 km pit do not permit (might even be less on some maps.)
For missile aircraft, engagement ranges make even 120x120 size maps too small and a very regular complaint and demand in the air communities.
In what non-arcade sense is it fun to use planes in an airspawn environment doing things they were not designed for in a tiny shoebox?
Even mid-vietnam era aircraft on cusp of BVR were not designed for the conditions of GRB (or ARB even), much less modern platforms (which even ASB fails to provide adequate play environment for)
Then give ground players the same mechanics as the combined arms naval game modes and ground arcade do: Random aircraft they can spawn for SP or kill streaks.
It is your problem because you’re expecting people to do things contrary to their purpose of playing particular vehicles.