Here's the thing (and then we should probably let the topic get back on point... I'm just as guilty):
As a fighter, you assumer certain risks when you pursue that line of work. You learn lots of things, but the most helpful are footwork and defense. Ronda didn't really display either.
As for Ali, that's a whole other conversation... But, I fought semi-pro for ten years, and never got a concussion. I attribute that less to "holy crap, look how awesome I am", and way more to the fact that I was super tentative about taking damage to the point of training my defensive strategies as much or more as my offensive ones. You look at a fighter like Dominick Cruz, and you see a guy who is going to have all of his faculties for a very long time. Marching right towards your opponent in a straight line with your hands down, especially when that opponent has a high striking pedigree, is either a sign of massive hubris or just piss-poor planning.