Roberto Duran was a naturally smaller man than Floyd Mayweather, yet he became middleweight champion when he defeated Iran Barkley.
Floyd Mayweather will never win a belt at middleweight because he will never take on an opponent slightly bigger than himself, like Sergio Martinez or Gennady Golovkin. However, Floyd has never had a problem fighting smaller men like Juan Manuel Marquez.
Duran never ducked anybody. His achievements are greater than Floyds. Instead of cherry-picking old faded fighters like Shane Mosley or flawed fighters coming off a loss like Zab Judah, instead of ducking prime lightweights, welterweights and middleweights, Duran was always willing to fight the best boxers in their prime.
Even fighters much bigger than himself like Iran Barkley!