You get excellence in a tiny number of individuals who don't budge the statistics. The national averages are poor, and the excelling individuals are not even numerous enough to create a "fat right tail".
Scientific and technological breakthroughs are created by the few. Always been, always will be. Fewer than 1 in 10,000 people are responsible for the current AI breakthroughs for instance, and I’m being conservative. You don’t need a fat right tail to completely change your country; of course, most of your tiny number of excellent individuals leaving for richer countries is a different problem altogether.
No, it's the same problem. Nobody wants to live in a country where everyone is impoverished and illiterate.
You do realize that if you go by "national averages" American math education is pretty bad right? People aren't leaving for countries with great national average in math. That's basically irrelevant.
This is interesting if true, but without data I can't take this claim at face value.