I agree that Roy knows his craft very well. But it really must be said that the difference in reflexes on one fraction of a second is what makes the difference between being Floyd Mayweather and being Arturo Gatti.
So while Roy could have been a good B or C level fighter with less physical gifts, that doesn't really mean much.
However, that being said, Roy did get by on athleticism more than anything else. He never comes in behind the jab, he never kept his hands or guard up until the very end of his career, he'd leave his chin wide open... but then, that's the difference - great fighters are great because besides working incredibly hard, they've got gifts that the rest of us don't.
Floyd Mayweather never fights behind the jab either -but he still leads with a left hook, which few besides Jones could do. Pacquaio is far from a conventional fighter - he punches from all angles and his hand speed lets him do that.
The great fighters are rarely conventional because they don't have to be, and being so odd in their style makes them incredibly hard for anyone - especially sparring partners, to replicate.
But then a strong example of a very textbook fighter who is also great is Juan Manuel Marquez. He doesn't have the physical gifts that the others have but he's technically so excellent, and he adapts so well, and he's so smart, that he can get away with it.
Being of mediocre physical talent myself, I emulate Marquez as much as possible because you don't have to be as fast as Roy or Floyd to fight as he does.