Its much more complicated than that. You see, most of the time you are looking it after the fact. Your are looking it once Usain Bolt has become the champion. In this rear-view mirror, you are explaining why is Usain Bolt so great at sprinting. And you find some of the genetic influences in it. May be he has much much higher number of fast twitching fibres to give him that explosive acceleration. Trouble is, this can only explain on individual's great performance. Another individual having a different advatange or a mix of advatanges may be able to out do this guy. Say a guy with lower number of fast twitching muscle cells but massive advantage in handling anerobic biproducts that hamper recovery (like lactic acid). So, he can train way more than past guy and optimize his running better. He simply does not feel impact of execise on his muscle like the other guy. So ultimately who has "better genes" or even what are "better genes". The answer is more complicated. It may just be possible to train a guy with different regimes to obtain very similar or better results if you know about their genetics and other properties better. Put it simply, there may just be different ways to skin this cat. There may be more than one winning combination. There may more than one combinations of training regimes and phyisiological features which can produce a world champion. It may in the end come to who got the right combination (not necessarily right genetics, there may be more than one sets of genetic traits equally good in different training regimes).
I remember reading about Micheal Phelp who actually has a peculiar double jointed bones that go an extra 15 degree IIRC (that may not necessarily a result of genetics or even heritable) which helps them achieve excellence in swimming which makes his feets behave almost like flippers.
Your gifts may come from more than one source.