I don't think social factors are not necessarily a nonfactor, more that this article claims that income equality within kinship groups is a forcing function for lack of economic growth. My claim is that the inequality that these countries face not just between each other within the nation but in our globalized economies, access to resources, capital and labor and thus the downstream effects of smaller markets, less need for labor will lead to less growth. I think you can have economic growth with kinship society if more people within the kinship have greater access to wealth growing, the issue here is that there's limited resources and the kinship society exists as an effect of less resources than the other-way around
> the wealthiest family of a kin group from 3 generations ago will be much more likely (relative to other cultures) to be the wealthiest family 3 generations from now.
I am not sure if this claim is true as well, wealth generally does stay within family lineages across cultures, generally people losing their wealth or even gaining it is an outlier. See any landed gentry in Europe, Asia
Actually; you can see this in America, as income continues to be more concentrated, and more unequal, economic productivity for an individual does go down as there's less opportunity to accrue wealth as before.