The only reason mma has evolved is because people have become more well-rounded since its inception. Other sports don't work like that.
There aren't currently running backs in the NFL as good as Barry Sanders was in the 90s. George Best, Pele and Maradona are still widely considered the best 3 footballers of all time and that isn't likely to change.
You've confused a young sport like mma where people didn't know what worked and what didn't, with old sports that have reached their own ceilings in terms of learning. With thinking like that are you gonna tell me that today's boxers handily beat people like Robinson or Hagler?
I wish i was alive in 100 years time when boxing has evolved so much that journeymen are better than today's P4P elite and they have to fight 5 times in one night just to have a proper workout...