Hmm....that's not how I've played my priest at all, but admittedly he rather came from a silver-spoon background within his realm as well and a bit of a buddha-esque giving up of imperial power to found the religion (meant to preserve an older religion from destruction).
I think, too often, religions fall into two major traps. Become too associated with realms and is basically used as an extension of the realms. Or becomes too disassociated from realms and thus irrelevant (usually those more focused on some *awesome* theology only they and a small group care about).
The way I've tried to play my priest is more like a spiritual advisor to the rulers and nobility on the state of the island, trying to push concepts/ideals that I/we think would improve the island. So there is a connection to realm politics without being an extension of another realm. To me, from a priestly perspective, I care less about the specifics of the realm (who wars who, specific person in power and their politics, who one allies) than the general atmosphere of 'are these virtues/values being fulfilled in this realm and what as a priest can I do to change that?' (there is a war or not or nature of war being gangbang/equitable or short/long distance, council talks to realm or is silent, realms choking island in alliance or not). It's more a cultural concept of shared values/ethos where we still disagree on other things and war based upon them, than an alliance of religious nobles working together or a group of players having theological roleplays or discussions.
I don't see priest and advy as too similar. Priests, as nobles, still have *huge* communication options. Advies just...don't. That is the crucial difference. If nobles didn't have the communication options they do, it'd be little different than the primarily click-nature of the advy (and the game would suck).
