"All else equal" means that PR volume is a signal that needs to be read in context a number of other metrics, as well as qualitative feedback.

You're absolutely right that PRs fixing things that a previous PR broke is a negative. Same for PRs implementing work not needed, or driving up tech debt.

"You're productive because you have lots of PRs" is a mistake without that context. But so is "You produce very little PRs, but that's fine, we shouldn't look at volume".

It's not a performance metric. It is an indicator worth following up. And there's a lot of reflexive "bad metric" arguments blanket dismissing that indicator.

Does that help explain?