I think there are specific reasons why it is not available for everyone at all times.
What those are? I don't know. Like you say, maybe it would be too easy and break the little mystic there is.
What I know from much earlier when I did play the priest game is the following:
- Elders are able to do a religion spread (from their own religion). At the time I played, this would give you a horrible looking map. (for example
The_Church_of_Sartan/Religious_Spread)
- A way for priests to inspect religion levels (all of them) in a certain region.
Anyone who actively plays or played the priest game, feel free to correct me.