Pernell Whitaker was robbed
Ike Quartey was robbed
Feliz Sterm was robbed
Also he lost just about every "big" fight he was in:
Felix Trinidad spanked him
Shane Mosley spanked him twice
Bernard Hopkins murdered him
Floyd "Money" Mayweather spanked him
Manny Pac spanked him
Maybe oscar is a bit overrated but his resume is better then ANYONE in boxing. No one fought the guys he fought, period. Win or lose. No one could go through that resume undefeated.
As for losing every big fight, no way man.
Trinidad - Oscar was ROBBED. Seriously man, Tito lost that fight.
Mosley - Oscar won 1 of 2 of those fights. The second one he should have got the decision. And Mosley later admitted he was on steroids for that fight so really it should be a No Contest.
Bernard Hopkins - was too big. Oscar had no business fighting the middleweight champ of the world. He should get props for even trying.
Floyd & Pac - at the tale end of his career. Cant really fault a guy for being past his best days.
And you obviously left out the fights he did win:
Ricardo Mayorga
Luis Ramon Campas
Fernando Vargas
Javier Castillejo
Arturo Gatti
Oba Carr
Julio Cesar Chavez (x2)
Wilfredo Rivera
Hector Camacho
Miguel Angel Gonzalez
Jesse James Leija
Genaro Hernandez
So no, he didn't lose every big fight. He won most, lost some, got robbed a couple times and got a couple gift victories of his own. But man, look at the names on his resume, it's almost unbelievable the talent he fought. There isn't a single fighter today with a resume like that, maybe the closest would be Holyfield.