the market they analyse is specifically self-published fiction. Most of the traditionally published books are not AI generated and they make significantly more money as a category than self publishing does. It is not really possible to flood that market in this form with 0 entry barriers.

So yes, allowing AI slop in a market where anyone can publish anything and quality is not a very strict criteria, of course it will dillute the market. But we are unlikely to see this shift in traditional publishing houses.