i dont think Manny has a bad chin...no way. Still he could get rocked by Cotto..it will have nothing to do with a bad chine. Hes going up in weight to fight bigger fighters...he has balls
You are describing the old Pac, he have improved on this greatly on his more recent fights. You are right about backing in a straight line which causes him alot of problems in the past but now he circles his opponent more as he backs off.
It is only a weakness when someone can capitalize on it, otherwise, its all theory. His weakness (defensive posture) is compensated by his strength which is speed and awkwardness, which makes him hard to time. He does not have the very regimented stance of a good defensive fighter, which is shoulder protecting the chin while throwing punches, and the other nonthrowing arm held high for possible counter, but probably he does not need to because his speed could make him get away with it.
pac's always had a decent(to good) beard, imo. guys like morales, barrera and jmm are'nt one punch KO monsters, but they've always been hard punchers. pac forgoes defense due to his open throttle fight style and get's stunned as a result, but he's never legitimately suffered a knock down in years.