My definition of “effective” is not sheer numbers. I am opposed to all calls to “just raise SP costs” for a wholly different reason.
No matter what the SP cost happens to be, one team will always get CAS up before the other. The other team on the receiving end will then always complain about being on the receiving end. Jacking up SP costs may make CAS less common, sure - but it also reduces the emphasis to use or even learn to use both CAP and SPAAG/SAMs due to the reduced presence of their intended targets.
Thus the few planes that do get airborne are ironically more powerful, not less. Which means the whine cycle continues until the planes are rendered irrelevant. Advance Mode rendered them functionally irrelevant, and surprise, surprise - the map said mode (Alaska) was tested on pretty quickly broke into an unbreachable line for the defending team more often that not.
The best counter to a plane is and always will be another plane, this is why having aircraft be restricted to “powerup” status makes them fundamentally unbalanceable. Currently SPAAG are too much effort for too little gains. CAS has no healthy purpose currently, being solely used as a griefing/revenge/anti-camping tool, and is completely lacking the vast majority of its actual targets. Idiotic game mechanics encourage CAS being used for petty revenge.
Hence, broadly what I would pursue instead would be far more thorough reforms that are actually thought through seriously. All calls for “raise SP” and “whur tenk-only mode?” are not being seriously thought through much at all, due mainly to the supporters of both arguments doing so in a state of angry frustration.
The idiotic mechanics encouraging CAS’s use as a revenge weapon need total removal. Most people on both sides cannot just calm down and think rationally while these mechanics keep everyones’ tempers so high.
The counters need to be made far more available, available by default like Naval already does, much easier to learn and use effectively for SPAAG/SAMs, made easier to defend themselves with vs tanks, among other things.
CAS (and tanks where applicable) need new objectives, which would also mean generally new maps to support those objectives. This would get the diehard supporters of tanks and CAS off each others’ throats, while also solving a number of tank-specific problems like spawn camping, not to mention making currently non-meta tanks actually relevant. There are also quite a few aircraft which have no mode at all to be relevant in since fighters or fighter-bombers do their job better - but more diverse objectives could help answer this.