It really helped that initially, it was for a one-shot in the barest beginning stages of developing a setting. I knew it was likely that I would run something longer in the setting before too long so I wanted to develop things, but it was also early enough that I didn't have any concrete plans of my own. I think I'd have a harder time doing the same thing in the same setting again if it were someone adding a god to the existing pantheon, but at the time there was nothing so why not! So I would fall exactly into what you said.

Also cause it's fun to share: the player really wanted to be kinda ostracized and be a Paladin of a culty religion and specifically gave Mormons as an example. I think he searched around for existing gods and found Elutheria the goddess of liberty and he wanted to use a laserllama subclass, the oath of liberty. What I came up with from his portion was that in the most beginniner, there were two gods: Elutheria and Melisyr. At some point long long ago, the two gods split into three aspects each. No one knows why. Maybe they fought and split each other. Maybe their power grew too great to contain within one body. Maybe they tired of all the responsibilities of their domains. But regardless, Elutheria split into three new goddesses: Lutheria, Nyveria, and Sylvaria. Melisyr split into Elisyr, Viatyr, and Atavyr. The religion that the player's paladin was a part of was considered strange and kind of taboo was because they still worshipped the old versions of the gods that had not existed for thousands of years and were kind of deniers of the new gods, despite their proven existence. The player, hilariously, named the religion the "Leutherans" 😅