Since moving to 147 Cotto has never demonstrated any issues with his chin.
In fact since the shift upward in weight Cotto has taken on his best opposition in Judah and Mosely, one an extremely hard gitter, the other among boxings most accurate live punchers.
In both fights Cotto suffered severe bleeding inside his mouth due to punishment, yet he never seemeed rocked badly.

I think this confirms the theory that weight drain was affecting Cotto at the end of his Light Welterewight days.