Never in the history of the sport has an elite, HOF-level fighter been as one-handed as DLH. I mean, you could argue Frazier, but Frazier had a better right hand than Oscar. Why in the world could Oscar never do shit with his right hand?
And he had a hell of a career in both the amateurs and pros for somebody "never doing shit" with one hand. Like any weakness a fighter may have it's not really a weakness unless opponents fully take advantage of it. It's not the same as an injury that a fighter or their corner didn't pick up on.
I haven't watched him in a long time, but my guess would be that, when he threw his left hook he kept the weight on his left foot. That is what Frazier did, he describes it in detail in his training book. You can't throw a good right hand unless the weight transfers from the right foot to the left foot. So if the weight stays on your left foot when you throw a hook....
Grey has nailed it as usual. No proper weight transferrence and his weight usually in his front leg. I get the feeling that had he stayed with Rivera a bit longer his right hand might have improved. Barrera is another who's right was a bit naff, but he improved it as he got older to the point of it being just about serviceable. It was though one of the reasons that Pac ran him over when the gap between them ability-wise was small imo.
Principally it's a combination of several things 1. He's a southpaw. He never had a big right hand 2. Necessity: he never needed one. He had handspeed and a left jab, hook upstairs and down. 3. Coaching . His coach was a yes man bum who couldn't teach a dog to sit. 4.Dedonnis. Oscar did not have the right arm of a Dedonnis. Once Oscar got with Floyd Sr, you started to see much better right hands a la vs Vargas. It's no coincidence that thats the fight Oscar's right shines in. A coach who knew the value of the right hand and its necessity vs an opponent who would be too familiar with the Left hook style for that alone to work. It's the go to fight for Oscars right hand.