> The large PRs needed to be large because they were adding features that couldn't be half-pregnant.

I'm not convinced here. I have worked on a wide variety of large, complex software systems throughout my long career. Never once could we not stage a large new feature using multiple PRs and feature flags. And before you pushback, remember that Google Chromium, which is objectively one of the largest and most complex open source projects in history, makes extensive use of this strategy for rolling out large features. See: chrome://flags/

"If there is a will, there is a way."