[anonyfox]

the unrealistic part of the whole narrative is: in that distant future he returns, another "hero" might step up and just kill him again, so he can't just "destroy all existence", or even Tamriel after some hundreds of years has modern/advanced military tech and will just obliterate a spawning dragon completely.

If something can be "killed" by a dude with an axe, it ain't a world-ending superpower for me. I get that Alduin could harass the known world by eating people or burn down villages if left unchecked, but "end of the world" for me is kinda different scale.

[PerryCox]

I think that is largely a difference between the lore and the gameplay. Alduin in lore literally eats all the matter in existence like a black hole. In the game he kinda goes against his purpose and wants to rule and feed on the souls in Sovngarde.