The irony is that's
one perspective on Abrahamic monotheistic religions, the one that's commonly thought in the West as
the one really valid and sensible perspective, because after all, we in the West know and understand Middle Eastern religion better than anyone else, including Middle Easterners or practitioners of the respective religions themselves. It's a blindly arrogant assumption too often made by those who in theory ought to know better than anyone else their own limited and less than objective perspective, the 'learned' scholars/members of academia in higher education, and it trickles down to popular culture.
Anywho, nothing to do with elves or orcs being insecure or whatever, it's more to do with my view that elves and orcs in
most fantasy genre/tropes are inherently, fundamentally and irreconcilably opposite, as different as fire and ice in
substance as it were, not merely perception/history/etc. like rifts and conflicts between RL human nations/cultures/races/members of the same species. In other words, they are TOTALLY secure and clear in the understanding of who and what they are, and that's why they hate each other so deeply and fundamentally

It's not the same thing as say, Arabs and Jews or Germans and Jews, whites and blacks who are all members of the same species, the same humanity; elves and orcs are so clearly and vastly opposite the other in most fantasy worlds that it would seem pretty incongruent that such beings could actually be paying homage to the same deity unless they both were deceived/deluded at a deep, deep level for centuries and millennia... which could be an interesting and unique twist certainly, but the author would have to be very clear that that is what's happening.
Certainly even Tolkien's 'orcs are irrevocably twisted, mangled versions of elves reflecting the worldview that evil is a twisted, mangled perversion of good' theme could be tweaked into 'maybe they're not so irrevocably/irredeemably twisted after all if they were at one time elves', and some of his unpublished writings supposedly reflect he experimented with that idea. But I would argue that to make a coherent, satisfying world/meta narrative, at some level the creator of the world needs to decide 'elves and orcs in this world might be worshipping the same god of war because xyz' or 'elves and orcs could
potentially be reconciled in this world like elves and drow because xyz' where xyz is a somewhat plausible and coherent, definitely intentional departure from most 'classic' takes on these guys.
At least do more justice to such elements than Greenwood and co. apparently did with various parts of FR theology where it makes you wonder what they were thinking at times, and lead to discussions where people go 'yeah I like lots of stuff about FR but the gods sometimes make me chuckle or cause my head to explode'
