I don't think Cotto's defense is particularly impressive either but let's cut the Margo fight out, and you know why. His defense in the first six rounds as he slid along the ropes and cracked Margarito flush the whole time showed tremendous skill. Two, let's take under account that Shane Mosley is an elite fighter, not some jerk who miraculously landed blows on Cotto because of his technical flaws. And Clottey? Yeah, his eye was torn up from Clottey's third fist (his head) and after that, of course Cotto wasn't able to defend himself that well. As for the other fights, it does seem to me like Cotto has slowly improved over the course of his career and he's a better fighter now than he was against Corley, Judah and company.
This logic doesn't change the fact that Cotto's defense is extremely leaky. I'm not debating that 2 of those opponents were overmatched. But look at what you just said, "Overmatched". Overmatched opponents hurt him VERY badly. Hardly a good defender. You just proved my point.
2 are bias prolly. I'd take Winkyince he's a boxing fan but he's fighting on PR nex so who knows but I kinda take him as neutral.