I don't think that human talent is completely homogeneous, there are certainly places where there is more of it than elsewhere.
That said, I think you underestimate many places. For example, Iran is one of the most ancient civilizations out there, and the Persian diaspora in the US is pretty productive, even though the country proper is a retrograde tyranny with very bad economy.
Iran is not very homogenous. Never was. Something very noticeable with the Iranians here in Denmark is that a lot of them think of themselves as well educated upper middle class despite having fairly average brain power. I've met plenty of nice and likeable people who fled from Iran but their talents don't match their self image.
