Do those studies actually exist? What are the odds that the societies with the exact opposite of what you say is healthy live the longest?
Genetic diversity is important, but you are making too much out of race. Superficial exterior differences between people isn't a measure of overall genetic differences.
I never said it was, but taking my ancestors for example, they came from a place where West Africans, East Africans, Arabs, Celtics, Iberians, Turks, and to Persians fought over that plot of land for millenia. The genetic diversity thete cannot be matched by somewhere like Iceland. Whilst Iceland as a high HDI, because stability has allowed a progress, they don't have the genetic bedrock to withstand a SHTF event. Iceland is a good example, because they actively and proudly practice eugenics against their unborn to weed out regressive genes.
Similarly, if you look at central American, from the various Amerindian waves fighting for control of the lush and fertile region, to the arrival of Celtic, Germanic, and Iberian colonialists, West African slaves, and then East Asian and South Asian servents. This is a place where the traits of any regressive genes become inconsequential.
The only force greater than this in nature is accelerated 'unnatural selection', like what happened to the slaves brough across the Atlantic or the Pasifika who island hopped across the Pacific. The weak genes died out due to attrition, and the strong genes of the survivors repopulated.