I think Good r rating is less about gore and explicit violence and more about content/context. I don't need to see a bunch of blood and viscera, this isn't a b-rated horror flick. What I do want is carnage to be terrifying. Thats what's hard to do in a pg-rated movie where the rating says it's aimed at teenagers.
Logan, for example had plenty of blood and stabbing and all that, but what made it a good movie was the context about a man loosing his own value at the end of his life. His own desperate search for self-worth and what it leads to.
That's a firmly adult concept that teenagers don't get or care about.