I worked for a human for a while who complained the same way. Problem was: it was a religion for him, not based in any reasonable logic. The large PRs needed to be large because they were adding features that couldn't be half-pregnant. The feature needed to be implemented fully in order to demo to customers or management. Once you have the whole thing coded and working it makes no sense to artificially split it into smaller pieces. That's unnecessary work you're doing only to satisfy the bloke with the beef about large PRs.

Anyway, absolutely none of that had anything to do with LLMs -- it was a function of a person who liked to control other people as much as possible. With LLMs I find they positively like to attack problems in small pieces. I can't recall ever having to ask one to subdivide the work. They usually just do that anyway.