Well it really depends what your goals are, right? What kind of books are you reading, to what end? I personally struggle to think of any book I have engaged with which I got value out of, that could be meaningfully summarized in a couple of hours. The author was an expert on the subject and they only managed to summarize it down to a few hundred pages - if there was only a couple of pages worth of ideas in there pre…
I find that most of the things I read can be pretty effectively summarized in a single thesis sentence and a few additional sentences to generally describe how that thesis was supported. If you're only reading things that can't even be summarized in an abstract, you must be reading a lot of unopinionated biographies?
But reducing a book down to a single thesis minimizes the takeaway value of the book, surely?
Take a book like Gödel Escher Bach. Sure, that book has a thesis. But the value of having read that book is not captured in ‘strange loops are all it takes to create beauty, complexity and consciousness’ - all the different ideas that underpin that thesis are what makes it valuable. That book lives as a set of new connections and pathways between ideas in my brain. And I read it over 20 years ago.