If you're going to get "sciency" about it, then you can't simultaneously have Ryne splitting into two visually identical entities (logically must be halved in density to remain the same size) and be concerned that the ancients would not be able to support their bodies with 1/14 of their strength. If strength is reduced and weight reduced to match, then – setting aside the properly sciency technicalities of how such things interact at different proportions – there is no issue. Their altered strength matches their altered bodies and all is even.
Or to look at it another way, if they all collapsed under their own weight and died immediately, the modern races cannot be descended from them.
Of course, you literally cannot halve "everything" about a person, numbers-wise. Halving the height of something while keeping the same proportions brings it down to an eighth of its volume. So there's a degree of ambiguity in exactly what would be reduced and by how much.
I have wondered in the past, but haven't fully investigated, if the relative size of human and ancient might work out to them being 14 times the volume – that would add up if the ancients are a little under 2.5 x the height of a human, which from memory sounds about right.
Actually, there's at least one example of Emet using "dark" in the same positive connotation that we would normally use light/bright – specifically from the Dying Gasp: "dream now of a dark tomorrow" to mean a hopeful one for the ancients.
I had a lot of trust for Hydaelyn and how Hydaelyn was presented to us, because I thought to invert it at such a late stage would be poor storytelling.
Even at late post-Shadowbringers, she seemed to be a primal designed to act as a mother-goddess, and it was conceivable that the narrative was designed to maintain her as ultimately "good" and the Sundering some kind of accident, A.I. logic failure or urgently needed as the lesser of two evils.
Quite frankly, the writers failed to take any of these paths, diminished Hydaelyn from being something "bigger than us" to just a single person putting on an act, and gave her a motive that... well, aligns with what the game presents as thematically good, but rings hollow to me.
I'm not questioning this narrative of Emet's because I support Venat; I'm questioning it because it contradicts what Emet himself told us in the game.