I think Quartey is fortunate that he fought in a time when fighters aren't as good as they should be, and that he did one thing in particular that really limited him as a fighter. Everybody talks about his jab, but this is where he screwed himself.
Watch him when he jabs, how he leans his weight way up on his left foot, to the point that the right heel comes up off the floor. That makes it impossible to throw the most basic combination in boxing, the 1-2. He had to jab, then rock his weight back, then throw the right hand, making it a 1-and-a-two. Also, jabbing like that makes it imppossible for him to close distance behind thew jab, for the same reason. He jabs and leans forward, then has to rock back, then step, then jab. This really cost him in the DLH fight.
Fighting really good fighters, that way of jabbing would have gotten him knocked out. They'd have timed that motion, that move to put the weight on the left foot, slipped the jab and hit him with a hook or right hand and stopped him. That said, Berto, Ortiz, etc...aren't good fighters so Quartey, being better, would beat them. Mayweather may very well ko him.