In addition to what Pangolin said. I quite often find the BRs where planes feel like they completely outperform SPAA are also the same BRs where I dont actually have an SPAA for that BR and so totally outclassed. (And quite frankly a 5.3 SPAA like the Skink should be useless vs a 7.7 CAS, likewise using an 8.3 SPAAG like the Cheiftain Marksman at 9.3 is naturally going to be far weaker than if I had a 9.3 SPAA to use)
But at BRs where I do have SPAA that is competitive, like 10.3 with the Stormer HVM and Tracked Rapier. I have very little issue countering most CAS and those that I struggle against are more often than not down to what Id consider bugs rather than actual imbalances (such as the IRST on the Stormer not working through a wisp of cloud)
So id say the biggest issue at a lot of BRs isnt that CAS is too strong, but rather that many nations have giant voids in their SPAA line and that forces them to either uptier their other vehicles for the sake of better SPAA or use a far lower BR SPAA and try to make it work, which, if the BR system is working even half right, should be a major uphill battle.
The only BR range where CAS vs SPAA balance almost entirely fails is top tier, with only one nation with a competitive SPAA system and even that struggles these days vs some threats. But that is hopefully being fixed (at least the start) next major update. Though this is mitigated by the multi-role nature of mosts CAS aircraft