Well let's see.... Mayweather beat Mosley who beat Vargas who beat Wright who beat Trinidad who beat Joppy who beat Duran. So yes a Duran win does indeed enhance Floyd's legacy!!!!!
I'd just take Lamotta here based on being a better middleweight than Duran and much bigger man. Yeah, Duran was able to beat Barkley, but Lamotta wasn't a brainless face-first slugger like Barkley. He had skills and ring IQ and a pretty underrated defense.
I don't know how Duran beats a guy who is bigger and whom he cannot intimidate or bully, and who is just as busy. LaMotta, close decision.