You need a bunch of things but without the genetics the drugs don't matter much either. You could even have a great drug response but if the structure isn't there, the long bellies aren't there, the number of fibers are few and the wrong type, you're going nowhere quick, no matter what. But it's hard to put percentages on all of the factors. Also, as Mentzer used to say, you can only properly judge the genetics in retrospect, gotta try and see, though some things you can see even in an untrained body, such as skeletal structure and muscle bellies, to a degree. One thing is for sure, you could probably bring someone to pro level in 1.5-2 years if everything is done perfectly from the start, assuming the genetics allow it. It's fast. Guys cycled and wasted lots of time in the past, and experimenting by themselves.