If I know what the book contains to write a perfect prompt, why would I need a AI-summary?

I don’t say AI cannot summarize or there is no value in book summary, but I’d say that by stripping off most of a book, you almost certainly lose something valuable about the book, even if it is a prescriptive nonfiction. This most valuable part (besides the advices) is very often the part that actually convinced you and help the arguments stick. And without that, information will just stay as information.