F-4C and A-5C might have a speed difference as you claimed.
But I still think it is not bigger than the difference between Jet and prop or Yak-38 and A-5C.
Exaggeration makes your claim weaker and makes things worse.
A-5C might be suffering in the current meta, as you think. It is true.
But it isn’t A-5C’s problem, but compression’s problem.
If A-5C can do nothing against a solid 11.7BR jet like MiG-23ML
It needs to be solved by sending MiG-23ML higher.
(Then MiG-23ML will suffer against F-15A, which can be solved similarly. We shouldn’t keep top-of-top-ranks like F-15E in 14.0 at all.)
I think A-5C is 10.65-ish jet currently.
slightly weaker than other counterparts in 10.7, but not bad enough to be 10.3
If you claim that A-5C needs to be lowered to 10.3, it can’t fight against MiG-23ML.
I can counterclaim with various subsonic jets in 9.3, which will not fight against A-5C in 10.3.
in short word, A-5C’s BR isn’t too high, other counterpart’s BR are too low.