No, as stated in my comment, there should be actions the player takes in order to expand the radius of his/her religious influence. These actions should not need moving little religious units around to fight each other. They could consist of researching religious buildings and policies (which diverts efforts in other areas that could be researched, like science or politics) and then building those structures and enacting those policies. To add focus and weight, the player could consciously devote a portion of his income per turn to religious expansion ("tithng") and that would come at the expense of other potential expenditures like infrastructure or economic growth.