Not warrior priests, but support priests that are behind the lines (like genral not some fictive red line), if player is smart, boosting morale before, and at the beggining of the battle.
yah, but how smart do you think the AI is.


Proof?

Seriusly, the way it is implemented, you would not fight with these units. They carry weapons just in case that battles lines get breached.
Again, it is impossible to prove something didnt happen, i cant prove romans werent really from mars cause not source will say "the Romans were not from MArs"

That means it up for you to prove that priest carried weapons with them on average.

Preist came in using all their might carrying some huge cross.