So, you played one game where things didn't go your way then make a blanket statement about something being impossible outright? I appreciate your frustration, but don't tarnish the games reputation over just one experience.
Well, I just finished my first BNW game with your same settings, but using Shoshone. My religion became the dominant religion with about half the cities following it and (now here's the kicker)
I didn't even touch Piety!
Using my single game as my sample, I could conclude that the religion game is too easy now, but I won't