"However, unless a galactic overlord designed the universe to please homo sapien rationalists, I don't see any compelling rational reason to believe this to be the case."

Except that we are free to adopt any version of rationality that wins. Rationality should be responsive to a given universe design, not the other way around.

"Irrational belief systems often thrive because they overcome the prisoner dilemmas that individual rational action creates on a group level. Rational people cannot mimic this."

Really? Most of the "individual rationality -> suboptimal outcomes" results assume that actors have no influence over the structure of the games they are playing. This doesn't reflect reality particularly well. We may not have infinite flexibility here, but changing the structure of the game is often quite feasible, and quite effective.