I appreciate what you have wrote. I did not mean to suggest you denied the obvious physical factors in Kessler's success. I also agree that, for his personal story and competitive development, his experience in rock-climbing seems to be playing a big role.
I think where we disagree, and where the main point of contention is, is the relative importance of these factors, and what it is reasonably possible for us to conclude. Everyone has to recognize the primary role that physical talent plays in phenomenal physical performances (and almost everyone does). But I would say that for the most part, and especially in the case of Kessler, who is relatively untrained and who's rise has been so meteoric, searching for any other contributing factors is essentially on the level of divination.
It is interesting that you brought up the issue of an American mindset, I hadn't considered that in the way you did. It is true that, to the extent we can speak of a national intellect, America doesn't really have one. There is a prevalence of illogical binaristic thinking, and Americans are generally pliable to (usually suspect) genetic determinist arguments. On the other hand, I view the exercise of endlessly checking the haruspices each time a new youth phenom shows up, trying to divine what factors, what novel training, what mental fortitude, what strategy, somehow explain and justify their success as rather American in style. We search for some kind of meritocratic, individualistic explanation of a phenomenon that might capture it in language, explain it, make it "fair". (Well, in these terms, I think this is a rather human tendency beyond just American). But all of this avoids the sticky and uncomfortable fact that the most reasonable explanation is the most frustrating - some people are inexplicably much better at things than others.
Anyways, I just mean to say that if we had any kind of broad empirical evidence, wether it be scientific studies or the more likely cumulative communal anecdotes, for various things (lifting, climbing, visualization, etc) improving running performance, that is all very well and good and interesting. (And yes of course we do have some of that evidence for some of these things). But the practice of divining anything meaningful from talents who exceed any logical explanation of their ability, meh.