Why is no one taking into consideration the high probability that in honesty, back in those ages, nobody probably gave too much of a honest stuff about religion except those who could genuinely profit from it
There's a distinct reason that I talked about my Warrior Buddhism as I did-- Which only consisted of it's spreading and the fact that no one forgeted with it, because it honestly had a distinct purpose that affected the smallfolk of Resu. It gave the people a chance to avoid being directly caught up in the middle of conflict, gave them food, and gave them shelter-- And honestly probably half of them in the sects probably didn't even really believe in the Warrior Buddhism as much as they let on. It was the one true way to get away from the prying eyes of the nobility, because as far as the nobles knew, they were a religious organization that fought for peace of the land, and would fight against any who tried to stop that
Aspidis did something very similar, they made a religion in which honestly half of them didn't really give a stuff about actually believing there was a god damn snake that gave birth to people, because it simply acted as a medium to allow profits of both people in high status' and small status to prosper, in honesty it was just meant to keep people from being too depressed about death, because the government knew that if war comes and people are getting slaughtered left and right, that their sadness will change to anger and anger amongst the smaller people is bad. And all they had to do was make it look like they're a bunch of emos that worshiped a self impregnating snake with two heads that were alright with death to people off from it, cause they knew well that having the religion spread would kinda ruin the point considering is was meant to keep their own morale up amongst those who believed in it and those who didn't, cause when nobility died the small folk ended up profiting from it from the wealthier churches, who would just say "yo that guys dead but you're alive, have some bread and go do something while you're not in the ground."
Oh and they spewed reincarnation amongst the kids so they weren't as afraid to die if they joined the armies, that kinda helped out with things as well
All in all, what I'm saying is it's more realistic to assume people honestly don't give too much of a forget about religion if they don't profit from it in some way. Resu profited from it with tons of stuff, aspidis not so much but it still worked out. Christianity just gives you a pat on the back and tells you to not be a cunt at the most, and then they go and burn your dead uncles corpse because they saw a rat on it and don't want mutated ebola.