[Book] was written by humans, perhaps many that didn't get credit.

As such, why do you care if book is written by machine?

??????????

Are the two scenarios not completely different?

"[An LLM] can fill out the details from a high-level schematic, which is probably, at best, what the author was doing with other team members."

If this is what you think writing is then why ever read a book at all? Just read the summary.