I think he was a very good fighter. His popularity was unmatched. He fought a lot of little guys and lost the biggest fights. I would say he's borderline.
pound 4 pound, probably not. what he's done for boxing is unmatched. if he was the coward and ducker that many fighters are then many great fighters like manny, may, mosley, would not have the exposure that they have now. de la hoya may have lost to many great fighters, but at least he fought them. even my favorites mayweather and hopkins are guilty of ducking people.
Insane amount of talent. Might have rushed into offence a bit too much after he turned pro, but Riviera seemed to iron that out. Talent, a money shot, and a whose who resume of fighters. That more than qualifies him as an ATG.
top 45 Jorge Paez John John Molina Rafael Ruelas Genaro Hernandez Jesse James Leija Julio Cesar Chavez x2 Pernell Whitaker Hector Camacho Miguel Angel Gonzalez Wilfredo Rivera Ike Quartey Oba Carr Arturo Gatti Javier Castillejo Fernando Vargas Luis Ramon Campas Felix Sturm Ricardo Mayorga SD loss Mosley UD loss Mosley MD loss Trinidad SD loss Mayweather KO loss Bernard Hopkins (Hopkins was a much naturally bigger fighter) TKO loss Pacquaio (way best his best and fighting at a weight he hasn't fought at for 8 years) THAT is a great resume.
I stay away from lists... but I do consider him an all-time great. It doesn't matter that he lost a few or had a few close wins... he had enough talnet to compete with anybody from 130-154 and plenty of 160 Lbers as well. He beat Jeff Mayweather (KO4) in just his 5th pro fight. Mayweather was 23-2-2 at the time. He went on to beat- Jorge Paez KO2, John John Molina W12, Rafael Ruelas KO2, Genero Hernandez KO6, Jesse James Leija KO2, Julio Cesar Chavez KO4 and KO8, Miguel Angel Gonzalez W12, Pernell Whitacker W12 (his first real close fight), Hector Camacho W12, Wilfredo Rivera KO8, Ike Quartey W12 (great fight, close fight), and Oba Carr KO11 His first loss was to Felix Trinidad L12 (a very controversial decision) He beat Derrell Colley KO7 then lost a split-decision to Shane Mosley in a great fight. He went on to beat- Arturo Gatti KO5, Javier Castillejo W12, Fernando Vargas KO11, and Luis Ramon Campas KO7. He lost a very close fight to Shane Mosley when they fought again, L12. He beat Felix Sturm in a very close fight at MW. He lost to Bernard Hopkins LKOby9 at MW but put up a great effort. He went back to 154Lbs and beat Ricardo Mayorga KO6 before losing a split-decision to Floyd Mayweather. He beat Steve Forbes W12 then lost his last fight to Manny Pacquiao LKoby8 at 145Lbs. At 5'11" with a 73" reach Oscar was a very powerful and durable JLW (only fought 4 fights here), LW, JWW, and WW. At JMW he was still very good but his punches seemed to have less impact. He was good at MW but only fought twice at that weight.
Personally I despise these "lists" and atg "rankings." They are always based on way to much speculation and subjectivity. 147 and below a prime ODLH was hell on two legs! He was pretty damn good at 154 too. One of my favorites.