I had this exact conversation with my boxing coach a while ago. Duran was my pops favorite fighter but he was before my time...so my coach makes me watch a bunch of his fights.
I think that people saying Duran has no chance never saw him fight. He is faster and a harder hitter than Castillo...plus he has better head movement and defense. Another thing he does well is make you fight his fight. I can see him turning the fight into a brawl and putting the pressure on Mayweather.

at people comparing him to Mayorga and saying that one of the best ever is overrated
On another note, Mayweather really lost that first fight to Castillo. I remember watching that fight with my pops telling him how great Mayweather was before the fight and then admitting that he lost....and an injury is not always a valid excuse cause I promise you that almost every fighter at that level has an injury, they just dont reveal it.