If HBD is true, then all the existing correlational and longitudinal evidence immediately implies that group differences are the major reason why per capita income in the USA are 3-190x per capita income in Africa, that group differences are a major driver of history and the future.

All true. But all the same is true if HBD -isn't- true. It doesn't matter if some of the group differences are genetic in origin, given that others are not, we can still resolve those.

that intelligence has enormous spillovers totally ignored in all current analyses

Assume HBD isn't true, and measured intelligence differences are purely the product of cultural and nutritional and parasite load differences. Now assume HBD is true, and measured intelligence differences are the result of the above and also genetics. Do the implications here change?

This has huge implications for historical research, immigration policy, dysgenics discussions, development aid, welfare programs, education, and pretty much every single topic in the culture wars touching on 'sexism' or 'racism' where the supposedly iron-clad evidence is confounded or based on rational priors.

And here I disagree: Regardless of whether or not HBD is true, we should still be taking steps to increase intelligence, for example by iodine supplement distribution, and reducing parasite loads. The steps we should take don't depend on HBD being true or false.