Also, there's an enormous leap from "they're not incapacitated... " to "they can do whatever they want!"

Yes.

In which case, the "incapacitation" you refer to is actually a vicious cycle, a structural problem, that's aid-solvable.

Surely some part of it reflects such positive feedbacks, but not obviously all. E.g. public health aid is not very well-suited to overthrowing kleptocrats and replacing them with efficient institutions, or changing cultural norms.

Also, note that there has been a Flynn Effect in Africa too, and it's one of the only regions of the world that still lacks broad iodization of salt, and thus suffers from the associated IQ deficiencies and retardation. Likewise for iron..