Interesting to pit that against Adam Curtis' contention,
"At its heart, South Park has a touching faith in human beings. That despite their absurdities and flaws, people have the capacity to create a better world."
Perhaps we can consider both this and
@boxedjoy's assertion to be correct. In this case, I'm using their words as a springboard to dive into what they could have been trying to say. So its gnosis, and not science.
Instead of considering postmodernism as a disappearance or withdrawal of sincerity, what if we consider it as a burying/cocoooning of sincerity within layers of sufficient skepticism, bureaucracy, distancing. Such that there is a wide sort of cortex surrounding the sincere core, and building of this cortex is a sort of alienation of the core from its cosmos.
In that way, perhaps South Park can be considered as a nugget of genuine and fundamental hope, dressed up in layers of skeptical defenses, facades. Perhaps even handled as an absurdism.
Analyzing the jump between the stage represented by South Park and the stage represented by Rick and Morty could be interesting as well. There was some theoretical stuff I was exposed to about Rick and Morty capturing some metamodern zeitgeist, and that would be part of the hypothesis here.