Make factions have "beliefs" which improve the pops more than happiness bonus and unity.

[tanny]

For example, materialist faction pops might have better research and produce more weight for scientist leaders and so on. Maybe even special buildings at some level of following.

In civ games, religions have beliefs. Beliefs influence stuffs.

 

[Metallichydra]

Sounds like a complicated way of making ethics give their bonusses.