This isn't an organized religion, but weaponized religion. The Sayer faith is all about love, so it's inevitably the most popular religion. It wouldn't be wrong to call the sages parasites rather than believers as they themselves don't belong to the upper echelons of the Sayer Faith.
And the most important thing is that the center of command hijacks divinity centered around "Sayer." And yet, MC's priest friend is a devout Sayer follower and they can't track him. Now the question is: Does the goddess Sayer exist or are there different methods of believing in her?