Those are two separate things, Ramiel.
I fully agree that religion should not be taken lightly, and that your character should not change religions like he changes saddles for his mount. It is very good that your character is making a gradual shift from a devout follower of the gods to an atheist (just kidding, just kidding, the point remains). The quality of such gods is a separate issue.
Tyr and Zisa could afford to use different names. It's like if I worshiped Yahweh/Jehovah and Jesus, Thor and Odin or Osiris and Amon.