I see Velen and Khadgar as different kinds (or denominations) of the light religions (idk make it the Judaism, Christianity, Islam trio since theres multiple light religions) trying to reconcile something about night elven religion (Hinduism for comparison) in their own worldview. Velen believes and interacts with the light and naaru, so he says she acts like one, which is not entirely wrong. Khadgar is more like if a christian dude read dome book about Hinduism and thought he knew everything, and his claim is not demonstrably false either.
I think perhaps sometimes people from outside the belief system will have the historicity and stuff like that more correct than pple in the religion, because theyre not attached. Elune could be a number of things, we do not know but the night elves have a specific idea of her, so do the tauren, and others. This does not invalidste eachother either, theyre all kinda equally guessing, even if the night elves might be right a bit more often.
Also the worship of Elune is a mystery religion of sorts, which is akin to worshipping certain greek deities by themselves in its hay day. There are also multiple sources of the night elves having multiple gods, Elune being one of them, and no im not referring to the wild gods. Elune is shown in a fresco in her temple forming the world alongside a pantheon of other deities whos faces are obscured, only hers is visible since shes the main deity in their religion. Does that mean shes a titan, no, but she may have been instrumental in forming Azeroth.