Gameplay should not be decided on hope, it should be decided on actual capabilities. Additionally, the change would be bad for gameplay as people would need to grind both their nation’s ground and air trees to be helpful to their team.
That’s not really true, especially with how much ammo planes have in their MGs.
Cost is not a factor that matters if you cannot shoot down planes, and once you die (because your SPAA is massively less capable of doing its job than a plane can do its own) you can’t use that crew anymore. That means you would need to dedicate more crew slots to SPAA, which both can cost actual money and/or means you need to use less-capable SPAA at a higher BR because your first was taken out.
Planes can also repair, only SPAA are immobile and defenseless when repairing (so CAS-food). Additionally, SPAA are much easier to kill than planes due to most being open-topped, having no armor, or having very light armor.
Things like turret traverse, the damage an SPAA does (and therefore its time to kill), the massive speed and maneuverability difference between SPAA and CAS, and the massive difference in ease of aim correction are factors constant to the vehicles. When looking at SPAA and CAS at the same BR (currently), a plane will have a quicker time to kill, be more maneuverable, be able to respond to and aim at enemies quicker, and have an easier time correct their aim than an SPAA.
This is not a scenario where you can just say “there needs to be more specifics” as a counterargument.



