He'd beat everyone but Deathwing and Archimonde without a sweat. The Lich King is one of the few characters able to routinely at will kill someone, my personal measure of a truly godlike being. To say that he'd lose to the elemental lords in quite the underestimate, as the elemental lords are roughly BAM (Big-Ass Monster, the foes Hercules slayed during his adventures) tier along with the ancients and aspects, powerful but not something that rewrites the goal of the conflict simply by existing. You can hope to kill a BAM, it's a common fantasy trope for heroes of legends to face a BAM in single combat and win, but a truly godlike foe is about moving the goal posts.