The lack of competition in a single market (in Miami, to cite your example) isn’t the result of monopolistic practices by the NFL, though. The NFL simply has a stronger brand name than any other competing football league, which means that the best players want to play for NFL teams, and the fans will pay more to see them.
Well, when they are allowed to buy out all the competing leagues, sure they are the largest league by far. Your eyes through the NFL are today. Go back to when the NFL acquired the AFL - should have never happened under anti-trust. It would be like Walmart and Amazon merging today.