Keep in mind that, when meteion wanted to hide herself by hyperthinning her aether, the ancients couldn’t even hope to sense her. Even we could only hear her through us sensing dynamis. It’s the same trick Thancred used to fool Ran’jit, actually… which ties in with a level 89 moment nicely, now I think of it.
Meteion heads to a place of pure dynamis, and fills it with her despair. To be able to even hope to beat her, you need two things, one pragmatic reason and one anime reason:
Pragmatically, you need beings that can at least somewhat influence dynamis. The ancients, though replete with Aether, can barely sense dynamis at all, or interact with it. They can indirectly influence it by tossing aether around, but if space travel was reasonable with aether alone meteion wouldn’t be an entelechy in the first place. Sending both enough aether to get them to her and empower them enough to beat her with aether alone is basically impossible - it took half the population just to plug the holes in the celestial aether. And if Zodiark leaves, the Final days begin the next day. With our thinner aether, it’s possible to interact with Dynamis and perceive it better.
The anime reason is you need people who not only can interact with dynamis, but who have experienced despair and overcome it. It’s no good to create an entelechy who’s never known suffering, like meteion was, because they’ll only be overwhelmed by the despair and not know how to deal with it. You could in theory create one that experiences suffering and learns to overcome it, but “we created you to suffer to deal with our problem at no cost to us” is… worse than even what Venat did, and classic tragic supervillain material.