Well we're not talking about career success, we were talking about comparisons of nation states. Having an IQ advantage there might prove marginally more helpful, but it's not really that important. I'd argue physical size and strength of a people are even more important than IQ when we're looking at across the board averages. Plus you have things like, idk, access to raw materials, geographic advantages, cultural advantages or disadvantages, systemic advantages or disadvantages including strong or weak institutions, training programs, etc. In fact, if you wanted to do a comparison between America and China you'd really have a lot better things to look at to show China as better than IQ.
With respect to "career success" you can have 50 million people in your country with IQs >140 and there's still a limited market to sell to. There are diminishing returns on capacity - you can have business analysts or call center folks with the IQ of Einstein and they'll be limited by the systems they are placed in.
The other side of this is that just because you are smart doesn't mean you are capable of doing well in the real world. Recall how there are a lot of "dumb rich people" and "smart poor people".