Tony does have an amazing chin but i dont think Cotto is a huge puncher at the elite level. All the top guys he has stopped have been stopped before or since.

He hits hard 4real but he is a break you down kind of power puncher and to do that he needs to get close and in doing so leaves that chin open.

I just wonder weather Cotto chose to fight against the ropes or that Tony cut the ring down that well he couldnt find the centre ring.