Look, if you don't think code review is worthwhile, don't do it. Just give everybody unfettered permission to merge. But don't pretend to do review if you're not trying to maintain some standard of quality.
A cap on PR size isn't inherently going to make an LLM do a good job of segmenting PRs. It requires careful prompting or manual action, the kind of effort typically exerted by people who already cared enough not to hit such a cap. You may as well just ditch the cap, to save yourself from having to reject a series of PRs rather than just the one.