Dorian's genetics in terms of size and the ability to put on muscle were not better then any of the mass monsters from Nasser to Dillet but one thing he had above the rest and it was sheer luck that someone like him would have this characteristic, as I do not see it having anything to do with race is the ability to not hold subcutaneous water under the skin.
Even in off-season he was bone dry, it was simply his genetics, of course the drugs enhanced this but give any one else the same thing and they still would not be as "granite-like" as Yates, unbelievable in person, his skin was transparent and you really would have had to have seen this in person with your own eyes to know how much of a difference this made.
The only one else who came close to this skin texture Yates had was Pavol Jablonicky, again even with Pavol you would have had to seen him in real life to know how dry he really was.
Now as far as race and genetics for bodybuilding, it is real hard to tell. Blacks win hands down in upper body, bone structure and shape, Germans and sourounding areas win for sheer mass. Really though, a freak can come out of anywhere anytime. Are British bodybuilders good?, yes, I think they are up there as well.