This is again just speculation on what I can remember from the story, but the way I understood it from what we've heard is that Hydaelyn was weaker than Zodiark because of the nature of her summoning having FAR fewer sacrificed lives to fuel her, and the only option available was sundering the world.
Ofc I do think it goes further to show the Amaurotines are every bit as flawed as we are, though that's a bit of a side note. Their solution to stopping sacrifice was more sacrifice, the solution to preserving new life the continued sacrifice of old and the possibly inadvertent sundering of *all* life. Hydaelyn certainly accomplished their original goal of stopping Zodiark from sacrificing everything else to resurrect the dead Amaurotines (not clear on whether only Amaurot was participating in this mass sacrifice? They certainly seemed to talk about the first city affected by the calamity as a separate entity but given the situation I could see it being all Ancients)... buuut at rh cost of sundering literally everything including the new life AND whatever few Ancients survived all this human sacrifice.
I don't trust Elidibus one lick but if half of what he's saying is true, Hydaelyn is too weak to do much of anything other than shouting blindly, hoping someone hears her, and either convincing or manipulating/tempering people into helping her. All working because she is the "mothercrystal" and viewed as such by the people alive today - which is interesting to think about actually. What little the world "remembers" of what happened millennia ago is of Zodiark being bad and Hydaelyn being good - cue Emet's monologue about the Victor writing the histories...
Anyway. All of this, imo, points to neither primal actually being inherently good or evil, but rather having fundamentally opposed goals, having been borne forward by people (Ancients) with fundamentally opposed philosophies. I got very much of a 'preserving the past at the cost of the future' vs 'preserving the future at the cost of the past' vibe from it all. Simplifies it a bit, but the heart of the issue felt more like a question of which life should be preserved - or, from the apparent perspective of the Ascians, which life is *worthy* of being preserved. Neither has the goal of simply destruction for destruction's sake, but Zodiark's victory would necessarily require the destruction of everything we (the WoL) know and love (or at least vaguely care about depending on how you rp your WoL

)
Basically my thoughts are we're gonna have to maintain the balance at the end of the day. If Zodiark wins, we (the WoL & co.) all die, but if Hydaelyn wins absolutely, there's every chance that the result would be the same. Zodiark is the heart of the old world, Hydaelyn is the heart of the new, and losing either could be catastrophic for everyone. That's what I think the end result will be anyway. I'm not sure destroying the primals will turn out to be the answer, but I guess we'll see haha