The people who don't watch MMA list would probably be the same as the people who watch MMA list. MMA fans who watch MMA tend to know all the fighters, including the casual popular fighters like Brock. But the fans who don't watch MMA tend to know specific fighters like Ronda or Brock because Ronda was in movies/ellen and Brock was a wrestling entertainer.
So Brock is known by both the hardcores and fans who really don't watch MMA. Fighters like Fedor are known by people who watch mma.That makes Brock more popular in general, because both the hardcores and the fans who don't watch MMA know him. Same for Ronda. I'm assuming when we are talking popularity we are talking about "known" and not "liked".