Should I ever play 4e Zeitgeist, this kind of "ecumenical" attitude is what my character would take. Though a dragonborn, his parents came to Risur before his birth, so he is a native citizen; he served in the war and earned distinction (naturally, only barely recognized, because racism.) He's developed a syncretic faith inspired by the stories of his parents and his knowledge of what happened to the Elves. Treachery, greed, and disorder are an active and corrosive force in the world. Every lie you tell, every cruelty you inflict, every con you pull, it strengthens this force, tightens its grip. But protection, hope, and justice are also an active, constructive force in the world. Every smile you offer, every victim you defend, every life you save, empowers this force. And when that force is powerful enough, it will be divine.Another thing that only occasionally seems to happen is deities being worshipped under different names. While there are some instances of this in the Forgotten Realms (Talos being an aspect of Gruumsh, as an example), it's not as widespread as one might suppose in a given setting.*
This can happen for a number of reasons, as faith in a popular deity can spread far beyond the culture that originated it. For example, Inanna/Ishtar/Astarte/Tanit/Ashtoreth are all basically the same goddess, who eventually morphed into Aphrodite.
*I feel I should mention Amaunator/Lathander or Tyche/Tymora/Beshaba, though it's not quite the same thing.
Across settings, of course, this is more common, with the Realms (again) having a wide array of deities that come from other places (including our earth, such as various Finnish, Norse, Egyptian, and Sumerian deities, among others), plus things like Bahamut/Paladine or Tiamat/Takhisis, Lolth/Lloth, etc..
The Realms is also home to the only triune deity I can think of in D&D, Angharradh, while our own world had quite a few (although Angharradh is a hot mess of retcons).
I realize I could have saved a lot of typing by saying "The Forgotten Realms is weird", though not really- Egyptian mythology has examples of gods fusing together like characters from Dragon Ball, and you'll find many gods with different aspects in South Asia.
I have a friend whose campaign is somewhat based on this idea; the Elves and the Dwarves claim to be older races, but in reality it's all a lie. It doesn't help that Humans have lost much of their history and culture, and even their lands, as when the big undead army showed up to attack, the other races didn't lift a finger to help.One of the ideas that I wanted to mention in the original post, but didn't think quite fit in with the rest of it, was having a "Gods as Tulpas" world where Humans existed first, created the gods, and then the gods created the other races to fit their specific pantheons (probably through warping/corrupting humans). For example, the Human War-God could be Gruumsh or Bane/Maglubiyet, and then the new god would have created their servant race (Orcs or Hobgoblins) to embody their warlike nature even more than humans.
So the gods would be Progenitors for the inhuman races, but also "Tulpas/Egregores" of human creation. It would also explain why the other races are so similar to humans and why they can interbreed, because they come from the same ancestral species fairly recently on the tree of life.
On the point of mantling from the Elder Scrolls, I never understood why someone would want to do that. Sure, you get the powers of a god for awhile, but your personality is eventually more or less completely consumed by the god's identity, as shown with Sheogorath in Skyrim. Which is basically the same thing as dying.
One of the ideas that I wanted to mention in the original post, but didn't think quite fit in with the rest of it, was having a "Gods as Tulpas" world where Humans existed first, created the gods, and then the gods created the other races to fit their specific pantheons (probably through warping/corrupting humans). For example, the Human War-God could be Gruumsh or Bane/Maglubiyet, and then the new god would have created their servant race (Orcs or Hobgoblins) to embody their warlike nature even more than humans.
So the gods would be Progenitors for the inhuman races, but also "Tulpas/Egregores" of human creation. It would also explain why the other races are so similar to humans and why they can interbreed, because they come from the same ancestral species fairly recently on the tree of life.