In the United States of America we are free to practice however many religions we wish, polytheism has been a thing for a very long time, since the beginning of written knowledge the Sumerians, Egyptians, Greeks, Romans, Norse/Vanir, Aztecs and a bunch of other cultures… your thoughts lack logic and are misguided by the desire to nerf the game. Begone troll.
I could get on board with the idea of monotheism in this game as it applies to summoning an avatar or creating the god protection. Like be able to practice any religion and craft all the gear and what not from any altar, but only your one chosen god will allow you to summon them, either for raiding or protection none of the others will.
except if you find the trainer. Each Religion has a location where you can talk t othe trianer and learn the first level for free.
I think that you are half right. Clans should be allowed to build only one type of t3 altar for their bases, but manage to build t2 altars of the other gods since they offer great bonuses! If they want to change the altar type, they would have to change the main religion and destroy their t3 altars in the process to upgrade any of the other t2 altars, which is a more balanced option!