Yeah, it's an optimistic biased system, but it's a decent practical approach. The cases of maintainers being lousy seems pretty uncommon.

AFAIK the reason maintainers can completely remove revisions of comments, is because occasionally a well intentioned user pastes sensitive info into a comment and doesn't realise.

While pointing it out to the user so they can remove it themselves does work, that's an unbounded time frame (perhaps never). So just nuking it directly is "safer" in that instance.

Doesn't seem like there's any really perfect solution.