>> the idea that all the most innovative people only exist in the United States (or even that people in the US are on average more innovative than others) is ridiculous, and stating it is just blind nationalism...
You couldn't be more wrong.
First, no one ever said "all" the dynamic people were in the US. The implied point was that the majority of them are. I believe that to be true for some very obvious, logical reasons.
The U.S. benefits from some unintended social and genetic engineering because of a few factors...
1. The U.S. has no ethnic culture (since Europeans supplanted the native population and then opened the doors to the rest of the world rather than embracing an "only European" ideal). So innovative people could more easily immigrate here provided there were advantages to doing so (which there were as I'll outline below). I'm not saying that couldn't happen elsewhere but a Frenchman who lives in England is still considered a Frenchman. A Frenchman who lives in America is considered an American and that inclusion makes people more likely to come here.
2. From our founding to the early 1900s the U.S. was far and away ahead of the world in recognizing and rewarding entrepreneurship. We didn't have an entrenched royalty or class system and democracy made sure laws benefited the populace in general rather than a ruling elite. This drew entrepreneurs to the U.S. and their descendants are likely still here (and in many cases inherited that dynamism either by nature or nurture)
3. From WWII to around the mid-1980s the U.S. was far and away wealthier than the rest of the world because WWII caused decades of damage to the European and Asian economies. Remember with the exception of a handful of planes attacking the West Coast there was no fighting done in the U.S. whatsoever. That means no reconstruction needed while the rest of the world was devastated. So again entrepreneurs (who are drawn to where the wealth is) came to the U.S.
4. The U.S. has a culture built around the idea that you can come here with nothing and become rich. That influences a lot of our laws and customs. For example, there's a reason why our tax rates are lower than a large portion of the world. So even today, when the advantages to starting a company in the U.S. are smaller than they've ever been, the U.S. tends to draw entrepreneurs to it.
So in the end it isn't nationalism it's just common sense.