Unfortunately, aside from being excessively wordy and light on supporting evidence for some of its assertions, it suffers from the same problem as this article and most of the comments here: people can't agree on what a genius is.
Debates about the foundations of genius are meaningless until we get a better idea of what a genius is. Some people, like this article's author, try to limit the term just to those people in history that have made significant advances in some field or another. But, then they cherry-pick their examples, usually from a list of their personal heroes, and then try to draw some conclusions from that.
Feynman wasn't a household name until really just a few years ago. Citing him as an example of a genius, and then going further to say that he was ("acknowledged by many to be") the last great American genius, is supremely silly. There are brilliant people right now working in every field; what do you think the odds are that, many years from now, after their death, at least one of them might be regarded as a genius by someone writing next century's version of this same article?
On the other end of the spectrum, you have Mensa, a worldwide organization of self-described geniuses, who even have a very serious test to keep out all of the non-geniuses. Should they not be regarded as geniuses? Why or why not?
If we're going to spend any time on utterly vacuous navel-gazing like this ... I think we ought to at least agree first on a useful definition for the thing we're trying to discuss.