It is not clear to me what the author is SPECIFICALLY against.

Only saying "LLM writing" is honestly lazy writing. Specifically what?

I get the glaring cases, I get the idea that if the prose is generated then maybe also the idea, I get the feeling when reading a complete LLM authored piece.

But that doesn't help the piece, because - beside those glaring cases - most writing today is a mix between authors ideas and LLM prose.