Where were the facts invalidated? Why can't a reader despise a writing style that LLMs converge towards?

I think you're right on your last point, btw, nobody will care and we'll be the poorer for it. Just like how McDonald's and Walmart have driven out and undercut localized taste and culture in the US, so it shall be with writing of all kinds. It's happening right now and readers are getting used to reading the intellectual equivalent of a Big Mac.