This idea is a really poor understanding of how athletics work, and it's something very prominent in America in part because they have a difficult time understanding that American Football is an anomaly in how its recruitment/prospects etc work.
Also, most football players are over 200 pounds, and most weight classes are under 200 pounds, so it already shows how little thought was put into this premise.
Third, most guys in the NFL really do not make THAT much money....and the guys who make the most play one of the least athletic positions available. They make more than they would in MMA, but their contracts suck ass too. NFL players are more "athletic" than NBA, MLB, and Soccer players yet make less than them...hm...maybe they should go there and "dominant" those sports.
Wrestling is an actual martial art or a component of fighting, and produces elite athletes, and America is a super power in that sport. Yet they are not dominating every weight class. So the idea that some left tackles are covering a blank space makes little sense. It's almost as if being great at one sport doesn't mean you can dominant another.
Wrestlers from America do not make a lot of money either, and many of them chose not to go into MMA because....fighting is different. Most of the best wrestlers in the world for example, have no interest in MMA or have no MMA careers.