1 Chavez wasn't a big puncher, he was someone that beat you down. 2 Did you ever see how badly he performed against southpaws ?b
Marquez' body attack did wonders for him against Pac - imagine what Chavez' would do to him. Pacquiao would be forced to fight on his back foot, and although he's recently gotten better at it, he can't beat a fighter of Chavez' caliber doing it.
I've said it before even whilst he was at FW and I'll say it again, no come forward style fighter is gonna beat Pac, unless there is a huge size disadvantage. Pac hits too fast, too powerful, too much, all from different angles. Pac is too fast on his feet, unlike Taylor who for a start isnt as big a puncher as Pac, Pac will do the same to Chavez except he wont stay there to get hit and trade like Taylor did, he will jump out. Pac will land as many punches as Taylor, but harder and he wont take nearly as much punishment in return.
How we know this? His only fight at 135 he looked sensational. Granted its against David "****ing" Diaz but Pac totally played with the brawler.