I largely agree with your observations, with the exception of your timing.
I think the forsaking was largely in place several decades earlier. The Catholics in the west in practice finished folding in the 60’s, but most everyone else of consequence in the west folded one to four decades earlier.
You aren’t looking at how Catholics vote and what it has done to America during the last 175 years, first in the cities and then when there became enough of them, states, and then nationally.