> Realistically, how much does merging vs rebasing actually matter - do you save days of time over the year, or just a few minutes cumulatively because the commit graph is prettier?

Excellent question! This is one of those how-to-measure-intangibles sort of question, so there's really no good answer to it. The issue is that bisection is really useful when you have a hard-to-find bug, and so the question is really "how often do you have such bugs", and the answer is hard to find because few companies require recording of such metadata in their bug reporting systems.