And all of them stated the violence was very much escalated in the books, is this not true?
So, in terms of "violent scenes," the book has the same key violent scenes (attacks from the bully, Bonzo, the weird stuff in the mind game, etc.) But the book also has a lot of introspection, characterization, context, friendship, and so forth BETWEEN those scenes.
That is, in the movie, the violent scenes seem to come pretty quickly, one after the other. In the book, they're more spaced out, so they don't seem as egregious.