BR isn’t based on projected future performance, outside of occasionally when reload / shell / ordnance selection is revised but that normally occurs when it would otherwise be moved downwards.
I’m sure if the Stormer ever becomes functional it may move around a little.
SPAA systems & CAS / CAP should probably be balanced around the equilibrium, where CAS gets a choice to either go after said systems or Targets, the reward for prioritizing them is to be otherwise unmolested and be able to attack targets of opportunity.
SPAA should serve as a backstop threat to encourage ordnance employment, or take advantage of an aircraft’s split focus due to Fighter CAP.
The reason CAS is in GRB is because most maps have exploitable power positions that take concentrated effort and concentrated teamwork to defeat, which is often untenable (take Domination mode on Port Novorossiysk for example ), and so to avoid stagnating maps due to their design, need some way to deal with that.
And as can be seen with World of Tanks, going the Arty route comes with its own set of problems.
The key thing I think needs to happen is to rebalance ordnance & clean airframe costs, to encourage varied ordnance and reduced loadings as a viable SP investment, for example.
Anti-Radiation missiles can only impact radars equipt vehicles, so shouldn’t cost much more then Iron bombs, they also take up a station that can’t be used for utility stores (e.g. Fuel / ECM pods etc.), or other ordnance. Later models (e.g. HARM, ALARM, AARGM etc.) also help minimize exposure risks.
My key point is that wining should require a varied team composition so having SPAA completely shut down aircraft, if it ever got that bad would only cause things to snowball, and be far more map dependent.
The Strela in this instance is was at too low a battle rating in my opinion since IR SAM’s are supposed to be best employed using ambush tactics , and as a last line of defense. not as a main element of said defense. Though I do feel that having Static spawn locations and the fact that average pilot not being very good certainly contributes to its apparent overperformance.