> The general consensus was that his own writing was preferable to the LLM's edited version.

I don't believe a single one of those people.

> For grammar, use a basic grammar checker, like the kind of grammar checker that has come with MS word since the 1990s.

Those are notorious for false-positives, false-negatives, and generally nonsensical advice. Not that the LLM-based alternatives are much better (looking at you, Grammarly), but still.