My two cents on that matter: I feel like we should account for heterodoxy and alternate religions altogether. My personal preference to setting mythology is an approach of "everything is true, and nothing is true." When religions and myth becomes accurate description of cosmology and history, it loses what differentiated it from science and study. Not trying to sound like I'm wearing a particular oft-ridiculed hat, but religion is truest when it is the best efforts of people to explain why the world is the way it is. Not that "true" cosmologies cannot be good or interesting, as the Elder Scrolls has an utterly fascinating and well-constructed mythos. Mostly because it draws from real religions such as Hindu and Gnosticism.