My sneaking suspicion is that there are a lot more cases than get reported, because authors are disincentivized to disclose AI usage, and readers by and large feel icky about reading AI work for reasons unrelated to quality.
I can totally see a weird future where a lot of what people like is AI generated, and everyone lies to each other about it. So it's hard to do research on this phenomenon.
I’ve experimented using AI to prototype game ideas and inevitably once I succumb to the temptation of handing the AI the game design reigns it starts devolving to meaningless slop with a silhouette of a meaningful design. The only way to get something meaningful (that ive found) is for the human to stay in the driver’s seat.