I was basing my opinion on how each fighter performed in the 80s- teh question is not entirely clear. If its a case of rating the careers then Duran is in 2nd or first
I think they may be basing it on what they achieved against each other. The fact that Duran only managed 1 win against the other 3.
That's a very simplistic point of view though, likely taken by those who don't have enough knowledge of the fighter's careers otherwise.