Well, one mitigating factor is that this hypothesis assumes that absolute or international countercultures work in the same way as intra-societal ones. There may instead be crucial differences between macro and micro cultural dynamics. Who knows? I'm just positing here that if there are cultural divides not just within societies but across them, so that we can speak of civilizational defaults and revolutionary breakthroughs on the international, overall historical scene, then the macro countercultures might be as fragile as the micro ones, assuming the social dynamics are similar.

Another mitigating factor would make for the best-case scenario, which is that before revolutionary secular humanism fades away, the coming compromised mainstream macro culture might assimilate parts of it, upgrading the civilizational default.

I like to think of it as being similar to coming down from a psychedelic high. Most of the insights are lost because the ordinary conscious mind doesn't easily integrate or remember them. But some peak states slip through the cracks and elevate the ordinary ego's perspective. Maybe something similar happens with societies in history.