I actually think "more PRs" usually does mean "better project" in the sense that smaller PRs are easier to review and reason about than larger ones. To me, though, I think the incentive here goes the other way - I'd want to put everything in one big PR so it looks like my client is getting a lot of work for their money. Either way, it's hard to imaging tying payments to PRs not having some impact on the coding process, which seems like a negative thing to me.