He's small and vulnerable for the real threats at 154lb.
Clearly, he's coming to the end of his run. It's just a matter of matching him in some nice fights that befit his current station (ie. balance the risk and reward more evenly) -- the Margarito rematch is the obvious one, with the added factor of its significance to Cotto's history.
These highly legit and hungry guys would eat him, and for what?