Not necessarily, if you're going to give Mayweather credit for beating the likes of Gatti, N'Dou, Vargas, etc. then you also have to give Pacquiao credit for beating guys like Larios, Diaz, Hussein, Solis, Sasakul, Ledwaba, Julio, Chae, Sakmuangklang, and a few others, so in which case the number of "quality" opponents they've each beaten is about even.
Legacy is just a part of an ATG standings. Floyd is more talented boxer but his legacy stinks comparing to PAC.