The difference in skill level is vast. He's got a great chin and great stamina like Hagler, nothing else. A lot of fighters have great chins and stamina.
Hagler has too much skill and was a very complete fight. Instead of watching his fight against Hearns, watch his great performance against William Lee or Tony Sibson, or the one against Alan Minter. The 80-83 Hagler was much much better than the one from 1986. Monzon also can't be compared to Margarito. Monzon was a slower, took his time and could break anyone's strategies with subtle tactics. The comparison of Margarito to Hagler or Monzon is simply awful.
Hagler lost a controversial decision to Boogaloo Watts, then a clear decision to Willie Monroe. He avenged both losses later on.