It's the punches that you don't see coming that hurt the most and Mayweather always had the speed to land those. So the answer is yes.
Accuracy and speed can knockout any fighter.The check hook he gave hatton can knock out anyone. Remember he broke that wrestler's nose (in reality)
At 130/135 yes. People seem to forget he had very good power there. At 140 he's an average puncher, and at 147 he has the bare minimum of power to get respect.
Compared to other fighters, PBF has good power. But what compliments his power and helps him get the KO's is his speed combined with the power. If you put him in the ring with someone the same weight as him, its likely PBF knocks out the opponent. But if he fought a Cotto, Margarito, DLH, Williams or Clottey, he probably wouldn't get the KO. It would be a very big risk of hurting his hands, and very hard to KO one of theose guys because they come in weighing anywhere between 160 - 171 on fight night.