You can compare cotto to a rapper. Started off as a very exciting attraction but slowly forgot his fans and became full of himself despite his career falling off bad. He was very lukewarm for the most part, never "horrible" but he was never "on fire" and great either. Part of it was his misfortune of sharing an era with two ATGs in pacquiao and mayweather but part of it was his own unwillingness to dare to be great and put it all on the line. Id rate his career a 6.5/10.
I think he dared to be great but always came up short. He fought Pacquiao, Mayweather, Martinez, Alvarez, Margarito, and Mosley. If he'd beaten them all that's a top ten ATG. He was very good but not great and his record reflects that. He'll only be remembered as an opponent of Pacquiao and Mayweathers.