Are you giving due consideration to the impact punching angles & handspeed have on the devastating effect of Pacquiao's shots? Tszyu didn't have those factors in his favour to the same extent, especially handspeed. I think they have comparable raw power, but Pacquiao is just flat-out the more effective offensive machine.
The main reason is because I was never a big believer in Cotto's power... I think he's a good puncher, but not a truly heavy one... to me, Tszyu clearly hits harder out of the two... Cotto is going to have more trouble hlding up to the right hands as the fight goes on then Tszyu is going to holding up to Cotto's hook... I also think that if you look at Tszyu, the main punch that always troubled him was the straight right, not the hook... Cotto needs that hook to work in order to win, I just don't think he'd land it enough
