It is harsh to say, but we need to increasingly recognize that if your writing is largely indistinguishable from the (current) output of e.g. ChatGPT on default settings, it doesn't matter if you used ChatGPT or not, your writing is overly verbose, bad, and unpleasant to consume, and something you most certainly need to improve. I.e. your colleague needs to change his style regardless.

This sucks, but it needs to be done in education, and/or at least in areas where good writing and effective communication is considered important. Good grades need to be awarded only to writing that exceeds the quality and/or personality of a chat-bot, because, otherwise, the degree is being awarded to a person who is no more useful than a clumsy tool.

And I don't mean avoiding superficialities like the em-dash: I mean the bland over-verbosity and other systemic tells—or rather, smells—of AI slop.