This topic is mostly for arcade ground battles, but you may find some elements relevant to RB as well.
I’m a big fan of SPAA tanks, they’re funny against light tanks and even some medium tanks. In fact, I find the SPAA guns a better experience against regular tanks.
Recently I’ve finding lots of people complain about how overpowered certain SPAA tanks are, mostly the 35mm armed tanks.
But here are scenarios to consider:
T-54 1947 vs MBT-70 (8.0 vs 9.0)
T32E1 vs T-55AM1 (7.7 vs 8.7)
STB-1 vs Magach 7C (8.3 vs 9.3)
M60A1 AOS vs TAM 2IP (8.3 vs 9.3)
In all of the above scenarios I described, it would be much wiser to use an SPAA tank instead of a regular tank, because of much faster firerate and the ability to damage something in a rapid, especially the tanks with thick/tricky armor and layout.
Not to mention, this BR bracket is dominated by light tanks, SPAA, and other lightly armored vehicles that SPAA guns suit the purpose better.
Finally SPAA tend to be faster and are more versatile, can deal with helicopters/planes. If you’re gonna die to a screaming speedy light tank with stabilized gun and APFSDS, then what does armor mean at all?
Conclusion:
Adding all these info from above, I theorize that the popularity of unconventional tanks, such as artillery and SPAA tanks, are partially caused by uptiers of vehicles with vastly differing performance (BR compression)
It’s harder to justify this on the individual scale (1v1 matchups you gave) because SPAAs struggle to penetrate most medium tanks frontally. This is true in the context of a match, however, given that SPAA such as Gepard are good at flanking.
I agree with the idea that unique traits such as fast turret traverse and fire rate make them retain their performance in uptiers, but it’s not necessarily better overall to use an SPAA.
You described the current Meta, for almost every battle rating excluding a few. Anti-air vehicles being versatile to deal with low flying aircraft, light armored, fast response time and firepower will clearly have certain dominance in-game.
For instance, TurnyPlays is one of the few people that acknowledge this issue in the balance in this video which is good to know that someone (someone that is heard) finally recognized this problem mainly enlightened by the XM-246 featuring, for the longest time, a buggy damage model that recieved little damaged when compared to other vehicles.
This isn’t something exclusive to arcade battles, I’m certain that this is a general balancing issue to be discussed and is not restricted to a single gamemode let alone a specific battle rating, I believe that the proposed armor piercing high explosive changes could’ve solved this issue even before said issues appeared.
There’s also just the whole aircraft being less rewarding than tanks so why not just run in and hope to get a few tank kills instead of sitting around waiting for an aircraft to come in range. Which tbh is the main problem, we really need score modifiers based on vehicle types
Finally SPAA tend to be faster and are more versatile, can deal with helicopters/planes. If you’re gonna die to a screaming speedy light tank with stabilized gun and APFSDS, then what does armor mean at all?
You can play aggressively in them. You have the tools to cover multiple roles - aka you don’t need to depend on your teammates to cover the anti-air role, and you can dunk on players thinking they’re the real ‘meta’ (who gives two shits about meta, anyway) in their little MBTs. It’s just fun.
It’s not surprise that Falcon and Flakpanzer are in my top 3 ground (RB) vehicles I’ve used this year:
