Yeah, I think Tolkien's Sauron is one of the things that's template-providing here more than it's necessarily the first thing of its kind. I should read some Conan stuff though, I never really have done.
And I agree - you certainly get people talking in revelatory ways about apocalypses in fiction, but they're invariably wrong in modern examples I've seen. So there's certainly very millenarian tones to how people e.g. discuss the White Frost in the Witcher, but ultimately the White Frost is a big doom thingy that needs defeating from the player and protagonist perspective. I guess maybe a closer revelatory example might be the Broken Earth trilogy in some ways? I think one of the really good things about the Broken Earth is its exploration of the concept, rare in fantasy, that actually there perhaps are things about its world that genuinely fully need breaking rather than simply defending from an essentially external threat or herding slowly towards an ambiguous better place. I think that's an interesting conception that's a bit different to the norms of the genre.