The catchweight is 159 pounds. That's what Sergio always weighs, 158, 159. How can the advantage be to Cotto? He was small at JMW he'll be even smaller against a MW.
Martinez beat the shit out of Chavez jr. Don't let the last round fool you. Chavez is very durable and has great stamina. Cotto is not durable (his face is as durable as wet toilet paper) and he doesn't have the greatest stamina. This was Chavez after he fought Sergio now imagine what will happen to Cotto:
You're banking everything on Sergios legs falling him. Against Murray it wasn't his legs that were the problem, the problem was Murray's high defensive guard. Sergio has problems against the high guard, peekaboo defensive style because he needs guys to open up to set up his shots. That's why he also struggled a bit against Darren Barker. Same high guard. Cotto doesn't have that kind of defense. This is a mismatch. I like Cotto, I'm a fan, but this fight is all wrong for him on every level. Martinez is bigger, faster, stronger, a better boxer, uses quick movement, better stamina. Literally everything is in Sergio's favor.