I think THAT Lopez could beat Margarito. I think Margarito's chin while very good, was proven to not be infallible. Taking too many Lopez powershots would have been bad for him. Lopez had the talent to be a champion, just lacked desire.
Lopez technically WAS a champion... of the WBO. But your point is taken. Lopez''s legacy was so close to being different... he was one good shot away from stopping Ike in the 11th.