Surely this could be corrected by using the correct prompt? If you ask an AI to summarise a book, it's going to cut out 99% of the content. If you wanted to read some of that 99% of the content, you need to be clear about what you want. Otherwise you're leaving the AI to decide. That summary might be good enough for others, but not you. Tell it the focus you would like it to use. E.g. "include anything about the philosophy behind the decision." Whatever your point of interest.

To be clear, a summary will never replace reading 300 pages. But it might be 95% good enough for most people and in most cases, and that's often good enough.