Exactly.
If you play the religious game for strategic reasons, then you're misunderstanding it. And I won't advance it into that direction. And that's also why it is optional and there are no drawbacks for not being in a religion.
While that's a coherent line of thought, I'd point out that if it's only meant to be RP anyways, why should people bother with game-handled religions? Most religions could have the same structure and advantages with a lot less costs by sticking with a purely RPed religion instead of one founded via game mechanics.
I, for one, stick with the old religions that have been up for a while, but I've completely given up on ever founding a new one unless things change. Been there, done that. Thousands of gold for temples, endless begging for funds, constant preaching which feels more like bureau work than anything, atrocious upkeeps, that only got worse now with the new taxes, to maintain medium to large religions, etc. All of that for...? Messaging? Sure, it's an advantage, but in most cases, all the followers are in a position that allows them to communicate with each other easily anyways. Religious maintenance tools? Takes months to convert well-populated regions, and with a single calm followers you typically end up losing a week's worth of converts for the gains equivalent to what a courtier would have had. Why bother? Offensive tools? Good luck converting enough followers to use it. And if you do, the damage is usually no greater than a looting attempt, may as well save your time and just come with a unit instead.
In some cases, it's worth the costs of founding a religion. In most of these, though, a single temple is all they'd ever need to satisfy their needs.
The approach of dumping all the religious duties on the priests is a problem, imo. On one hand, they are asked to provide all the RP to make the faith dynamic and alive. On the other hand, all of their tools concern *regions*, and not nobles. They feel like glorified courtiers. If you ask me, it's no wonder almost nobody wants to bother being a priest, and that a good chunk of those who do probably only do it for the hour/travel system more than anything.