Religion is a bit of a tricky beast. The point is that religion is a rather local affair, and that the same numbers mean different things. Two religions both having 100,000 followers can be very, very different if one has 5-10% followers everywhere and the other has 80+% followers in a few regions.
For religion, I am thinking about creating a "strength map" using the new dynamic map. I think that would be more informative.