The Amish don't seem particularly interested in this effect: they're growing rapidly. Same thing with the Haredi. This effect whereby "all high growth populations have eventually slowed their population growth as gdp capita and mean years of schooling increased" is a temporary phenomenon we observe while natural selection does its work and selects for those who are able to resist the fecundity-reducing effects of modernity --- people like the Amish and the Haredi.