I think there's a lot to be said for it. Particularly insulin/ HGH response.
In the old days you had the odd guy out who grew large aesthetically shaped beefy muscles that are, basically I believe, marbled w/ fat IN the meat like a cut of steak. Muscle that grew and stored fat INTERNALLY in that manner. (any pros want to volunteer for bicep biopsies?)
I think that the insulin/ HGH protocol some have got down, can transform the right individual to this, from scrawny. But, not everyone.
Genetics are everything. Look at Jay Cutlers teen photos. I was looking at some old Pics of Chick too - a born BBer.
I forget who said, "it's not just genetics anymore, it's genetics for large doses of AAS". I think theres something to that. It don't lessen the amt of devotion it takes to pull off developing it though. That's long hard work, period. But most of us are never getting there regardless.