>In fact, if you look at the accompanying map[2], you will immediately notice a strong inverse correlation between diversity and living standard. Assuming the underlying analysis of diversity level is accurate, this map itself is a condemnation of the entire ideology surrounding diversity.
As a matter of fact, this correlation is much weaker than you portray it to be, and the number of outliers in this hypothesis call it deeply into question. Let's assume GDP (factoring in purchasing power parity) per capita as a proxy for standard of living. Consult this map and compare it to yours:
https://en.wikipedia.org/wiki/File:Map_of_countries_by_GDP_(...
You see many counter-examples to your thesis. Africa tends to have poor correlation between ethnic diversity and standard of living. Look also at East Asia: the more diverse Indonesia and Papua New Guinea are doing better economically than their homogeneous northern neighbor in the Philippines, in this region too is diversity poorly correlated with economic status. Also true of Europe -- just look around the map and you'll find counterexamples everywhere. Look at Switzerland -- it's at once one of the wealthiest and most diverse European countries according to your map.
Your example of Japan as an ethnostate is also an interesting case study. I agree that it resembles an ethnostate. However, it's also going through a demographic crisis which is in large part attributable to its status as an ethnostate: an increasingly wealthy and aging ethnically Japanese population is an impending disaster in the face of Japan's historical (and contemporary) strict policies on immigration and integration.
Speaking of demographic crisis, compare your map to this one:
https://upload.wikimedia.org/wikipedia/commons/b/b7/2017_wor...
I see some correlations there.