Comments are ascribed credibility based on the trust the reader has in the commenting entity, whether the comment is consistent with the reader's priors and researching citations made in the comment, either explicit or implicit.
Since GPT can confidently produce comments which are wrong, there is no trust in it as a commenting entity. Consequently everything it produces needs to be further vetted. It's as if every comment was a bunch of links to relevant, but not necessarily correct sources. Maybe it produces some novelty which leads to something worthwhile, but the cost is high, until it can be trusted. Which is not now.
If a trusted commenter submits a comment by GPT, then he is vouching for it and it is riding on his reputation. If it is wrong, his reputation suffers, and trust in that commenter drops just as it would regardless of the genesis of the comment.