It becomes a problem when it is obvious that the LLM had a much bigger contribution to the writing, which is something that we do see a lot on posts here.
This is the same as LLM-assisted PRs (generally fine) and LLM-authored PRs (harmful).
I usually give two different AI's the same prompt for nuance. My problem is still that they tend to drivel on, as if a one word answer is not good enough. Still I would rather have them than not.