I've been deeply interested in this issue for years, and my impression is that IQ just isn't that strong a lens of analysis. It's incredibly difficult to prove which way the causality goes.

A quick example of this: There has yet to be an IQ test (that I'm aware of) that participants can't increase their score in by studying/practicing. This implies that groups with higher IQs may just be unintentionally 'studying' for IQ tests in their education/environment, putting the ball back in the socioeconomic/environmental factors court.

The validity of IQ itself remains a hotly debated topic, let alone how that might affect the development of nations. You're much more likely to be productive as a researcher of this topic, I think, by leaving IQ out. Just like this article, and these comments.