The inherent issue with what you’re requesting though is that air would become overwhelming for tanks and SPAA to contend with and if strike/fighters/bombers come into play faster, that shifts the mixed role gameplay of ground and air towards more of an air focus.
SPAA costs a nickel to spawn compared to a plane because most of the time, not everytime, SPAA serves a limited role. Sometimes they can be used to KO ground units if played in an ambush setup and can get capture points if they are left undefended, but these situations are hit or miss to come by and inconsistent. SPAA vehicles are also thinly armored and often are open top designs, which puts their crews at extreme risk to even small arms fire.
So, because their primary intended use is to shoot down aircraft, and they are typically lightly protected, they get reduced spawn points.
A properly loaded Tu-2 on the over hand is a vehicle designed to bomb targets like infantry, infrastructure, and armored vehicles. In War Thunder, its job is to KO ground units and it can do that exceedingly well. Its a vehicle for example, like many of the other CAS planes. that can theoretically KO multiple tanks, land, rearm, and repeat. Of course its going to cost more to spawn a CAS equiped plane than it would an SPAA. One Tu-2, as an example of an excellent CAS aircraft, has enough ordance to wipe half a team before needing to land.
If lower rank matches gained access to lower respawn costs for aircraft, we would see more balancing issues like those we see at high ranks between ground an air. Its not fun playing an MBT only to suddenly explode to one of the 6 aircraft 5km above the AO with AGMs.