I take what you're saying typerated, but the point is that with a magazine of 1,700 rounds (compared to 500 rounds for the F-15E and just 250 for the F-35A) the A-10 won't have to declare itself to be 'Winchester' after only one or two strafing runs.
I'm not a soldier myself, but I'd imagine it is the A-10's ability to loiter long over the battlefield, as much as anything else, that makes it such an effective and popular CAS platform.
As I said earlier, the calibre of the gun is only part of the story.