The part of Appalachia I grew up in for example, in Maryland, had among the best public schools in the state, and had among the highest testing outcomes in the state. That's still true to this day.
I'd like to see you prove your claim and define what a surplus of below average intelligence people means.
Given the small population base of Appalachia, you're not providing meaningful evidence of anything by referring to that location. The median standard of living in Appalachia is higher than that of Spain, Portugal, Greece, Italy, Russia, China, Latin America, and so on.