Thunderbrd
C2C War Dog
If that's the case, then we need to improve the AI a bit on that - I tried doing some improvements in that area a number of years back but was kinda crappy at programming and couldn't get it to compile so I commented out what I was trying to do - probably comments have been erased since then but maybe soon I can take another look at it. That said, some earlier AI versions would adopt a non-favorite religion but then if they GOT access to their favorite - and weren't TOO invested into the one they had adopted in the meantime - they'd make the switch. I'm not sure how they behave right now.Unless it has been changed, the AI will only adopt their favorite religion no matter how many they get. Not having a religion is very bad for almost everything, production, commerce, et al.
National religious strategy does seem to be a place we could greatly improve on for the AI overall. Original Civ IV (not even BtS) Vanilla was better at it than our AI is currently.