I have written several books the old way - before AI, and find that Writeseed does a really good job. I tried about ten of these, to work with demanding texts and it performs extremely well for a very modest price. Don't forget to play with all the options. My favourite: write a draft paper and put it in the prompt box of 'blog post' or 'ad copy'. To be clear: I'm not giving it just a few prompts but an entire paper and the results are extremely interesting.