Depends on how PRs function within teams. For some, the PR is a lightweight thing that is the preferred method of communication. It sounds like you are imagining a case where face to face communication, or communication over chat, is preferred for early stages, with the PR being a nearly final artifact. But it doesn't have to work like that.
I think that's a valuable point. Especially as LLMs bring the cost of prototyping down (and reduce emotional investment in code written), it may be more viable to use PRs as proposals/sketches of a solution.
With human reviewers, I find that by the time someone has churned out enough of a solution to post a PR, they are already quite invested in specifics of the solution, and it makes it emotionally costly (to both author and reviewer) when someone says "hey, I'm not a fan of this whole approach, lets start over and do it this other way"
I have seen many a PR where it is obvious it is an exploratory work: eg. figuring out how to use an external dependency that is imperfectly or incorrectly documented, etc. (You can claim this should be done ahead of time, but experience tells me you need to code it to learn it)
The emotional toll there is real, but this is exactly the moment when you expose the knowledge of that external dependency to the unbiased party that is the reviewer.
I like combining approvals to satisfy the urge for completion and closure, with a request for fast-follow refactor to better match the newly discovered model of interaction. (The worst code review experience I have seen is when a reviewer accepts it as-is and does a fast follow refactor themselves, depriving the author of the opportunity to learn and remain an expert in that area)