pr00ne,
There's more to an aircraft's gun than just its calibre. Your comparing the A-10's to "other 30 and 25/27mm cannon equipped aircraft" shows you don't understand that.
It's boneheaded comments like those that have fed the USAF's myth that the A-10 can be replaced by the F-35 in the CAS role.
obsolete slow non radar equipped heaps that the only Air Force that ever bought them has been desperately trying to junk for years
Thankfully, more informed heads than your own have prevailed every time they have tried.