Yabia Omer,
“I guarantee that a massive percentage of the families of people in Lakewood, for example, were not Charedi a couple of generation ago. Maybe not even MO….”
The development of the American Jewish world is not really a representative example. Until the early/mid 1900s, there was not much Torah learning available in the US (many European gedolim were opposed to immigration to America), so many immigrant families became less knowledgeable and more assimilated rather quickly.