A mainstream church that survives centuries must have a lot of instrumental rationality
This isn't obviously true. Once a belief system is established it is easily continued via indoctrination, especially when the indoctrination includes the idea that indoctrinating others is a Good thing.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)