I'm not sure, but I will say that I've yet to read an AI write in the style of Thomas Pynchon.

This is actually a great question, since best-selling novels are, most of the time, not particularly good, and rely heavily on trends and established patterns; precisely what LLMs are best at.

I'd say that a best-selling novel today is at least 50% luck and 40% author pedigree + marketing.

A good novel, thou. That is an entirely different thing...