Meteion works because there has always been a mystery as to what causes the Final Days. We knew only that Zodiark saved the planet from it but didn't defeat the source of it.
We've been getting hints that something isn't right with aether as early as ARR (I didnt play 1.0, sadly, so i have no frame of reference prior to ARR) in which the Scions are investigating a 'thinning of the aether'.
At the time, we are led to believe that the Primals being summoned is what leads to a thinning of the aether. Corroborated by the fact that Primals do in fact drain aether from the land while alive. So we assume that thinning aether indicates a primal summon. And then we find primals have been summoned.
But then we later find out that the aether is still undergoing a thinning event despite no primals being active anywhere. The Scions keep investigating that but can find no cause for it.
Then we get to Endwalker. During which we re-trigger the Final Days and learn one important factoid from Y'shtola, that when a person changes, their aether "crumbles and rots away". Begging the question, if aether is life then how does a creature exist without it?
That question sets up dynamis, of which we get a suggestion of what it might it be. But even before all of that, we have a suggestion of a non aether based emotion based power in the Elpis flower when Hydaelyn ensures that we recieve it in Labyrinthos.
So the comparison between the Jailer and Meteion's inclusion to the story is that there were unsolved mysteries being set up so that discovery of Meteion answers those mysteries, while the Jailer is shoehorned in with a vapid "The Jailer was behiind everything the whole time and was such a perfect strategist that he left absolutely no trace of his existence until now".
Oh and Meteion herself was that which was going to end the universe and we needed to fight against her despair to win, while the Jailer is "hurdur if i get to the thing, i will rule the universe!"