The danger in this assertion is that you have assumed that Mark Ripptoe is the only authority on the subject to be believed. You have assumed that he is right, but he might not be. I’m not an expert in athletic training, but I have my doubts about Ripptoe’s statements, simply by virtue of logic.
One test for rationality is the non-falsifiable belief. If one holds a belief and does not admit that it might be wrong, then one holds a non-falsifiable belief, and therefor is demonstrably irrational.
You (and Mark) cite genetics as the sole determining factor in elite athletic ability. This flies in the face of what other trainers believe. Why latch on to someone's ideas simply because they challenge the status quo? These ideas might be wrong. They might be based on fallacious reasoning.
Also (and perhaps more importantly in refuting your thesis) there have been many recent studies of genetics which indicate that a person’s genes are not immutable. It has been proven by peer-reviewed scientific studies that one’s genes can be changed! One of the most important factors in making genetic changes is belief!
I posit that this indicates that if one believes he can be an elite athlete and trains like an elite athlete, it might be possible to usurp the genetic makeup they need, and become an elite athlete!
That having been said, I think that you have done a good job of studying the issue, and presented an interesting case. Your argument is certainly not preposterous. It simply is not definitive.