I think the tech is advanced enough to recognize a user by their choice of words. Not to downplay the problem but currently a new user might start out with a few comments on the poor side then talk into the shadow realm indefinitely. In my not very humble opinion the asshole level of the poor comments can easily be lower than the asshole level of the response.

I wrote a fun solution one time where the document comes with a token that needs to mature for a duration depending on the user. Then, when your [say] 30 seconds are expired the input area is displayed but the submit button only appears if you input enough characters - where enough again depends on the user. If you are likely to make low effort postings I want at least 500 or 1000 characters worth of low effort. In even worse cases ill also hold the comment for moderation - until I get to it. (which might be a long time)

>the backstory has been that it's someone with a track record under other usernames.

This has gaps, as you know, and doesn't wash. Let someone turn a new leaf. Amnesty puts a stop to this.