Were talking about 1.5km effective range for platforms like Gepard, around 800m effective range for Vulcan and even less for WW2 vehicles.
Sure they can fire outside of those ranges and try to hit planes, but with WW2 vehicles that entirely hinges on the plane being asleep as to not notice tracers trying to lead him, as they have no fire control systems beside good old eyeball mk.1; with things like Gepard theres absolute range of like 3km where the HE shells self-destruct.
SPAA has to closely follow the tanks to battle to get as much effective range between their tanks and enemy planes as possible, which isnt always possible due to map design. Meaning sometimes SPAA doesnt even get its full effective range.
So if you think about it, while yes, most sub 9.7 CAS has to enter the SPAA range, if the CAS plane keeps its speed, SPAA has only short window to intercept it before it drops its payload.
And were not talking about things like supressing the SPAA first with unguided rockets, with enough speed and alt i can confidently launch HVARS or those Il-2 rockets towards SPAA at distances far exceeding the effective range of WW2 SPAA: or things like Bullups on A-4B, which can comfortably sit outside of SPAA effective range and sling Bullups at targets. Or the swiss Hunter which for some reason sits at 9.7 with two Mavs, which outrange any 9.7 and below SPAA beside the french Roland.
Team with bad* CAS.
Players that take fighter with single bomb, drop it and then spend rest of the game straffing ground targets is usually what loses the match.