[PerryCox]

In Skyrim they didn't send Alduin into the end of time, just into the future (also there is going to be an Elder Scrolls VI so V can't be the end of time, but will likely be the end of the fifth era). It was one of the reasons that the Felldir the Old was not onboard with the plan to use the Elder Scroll on Alduin. They didn't know how far into the future he would be sent. Most people on Nirn at the time of Skyrim didn't believe that dragons were real, much less Alduin who signals the end times. The Dragonborn ultimately ends up defeating Alduin, but because Alduin is immortal (in a way that the other dragons are not) he will return at a time deemed by his father Akatosh and actually destroy all of existence in that universe.

Going back to your original point it's a little different than sending him to the end of the universe, they sent him forward in time, but they actually had no idea how far or where there were sending him.

[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.