I feel like people only look at the form and ignore the substance of the content. Honestly, as long as the content itself is well written and the em-dash is used correctly, I don't think it really matters. When I first learned about em-dashes, I was told they were a mark of sophisticated, intellectual writing. But now people say they sound like AI. Is that really a bad thing? It's strange to see sophistication become…
The combination of both I usually find in text generated for me by LLM, and so far, it serves as a good signal for density of information and, inversely, not-quite-right ideas and their connections. (That's not to say it's pervasive, but below the surface, the quality of LLM text as a medium is often not great.)
There may be well-written text of non-trivial length generated by LLMs, but so far I haven't knowingly encountered any, with or without em-dashes. Human editing remains very necessary.