It's pretty stunning what the GPT models can / will be able to do with language, but we're still a long way from competing with professional writers. There's a big difference between coherent prose (which anyone with a bit of experience can write) and creating compelling original characters or tapping into the human condition. Great novels accomplish a lot more than just "good writing".

That being said, there is a lot of trash that gets published anyway! The AI may not be coming for Stephen King, but it will be coming for a lot of the mediocre stuff on Amazon.