How I've always thought about the book vs movie question as well for exactly those 2 points.I’ve not found one. Or at least I can’t remember one. I think it comes from two things. 1. Reading is such a personal experience where you create everything-visuals, sounds, etc and you are immersed while movies try to do all that for you and are therefore less compelling. 2. You just can’t put everything from a complicated novel into a couple hours on the screen and there’s no way to get the nuance without a narrator which is clunky and again not personal.
Funny that several have brought up Jaws as that has always been my poster child. Book had a lot more going on and the shark was simply part of several storylines. Obviously the movie was all about the shark but to your second point, if you're trying to fit the story for a "summer blockbuster" into 2 hours, they certainly picked the right "character"/storyline to emphasize.