In terms of overall competition, clearly DLH, who as someone said earlier, would be top 10 if basing solely on competition. As DLH has gone 50-50 against his best names, however, and Mayweather has stayed undefeated, Mayweathers stock rises significantly.
It depends on what you mean by lesser competition... If you're talking about Calzaghe-like opposition, I"d agree with you. But your also seriously underrating Mayweather's competition. Remember back in the days when he was fighting at 130 and 135, and ranked about mid-way top ten p4p? The very FIRST thing people would say about Mayweather is the quality of his resume. Now granted, ever since he moved up to 140 and became no. 1 p4p, he's done more picking and choosing. But who doesn't in his situation? And guys like Judah and Dela Hoya, and now Hatton, are still good enough names. Furthermore, you must take into account how the fighter who went 50/50 got beaten. If, the times he lost, he was thoroughly dominated or knocked out... Well, he doesn't get THAT much credit for his superior resume. As usual, it's very much not black and white