It's ultimately a matter of perspective and the writers themselves have stated as much both in-game and outside of it in various interviews that have been posted here many times already over the years.

I don't believe that Zodiark or Hydaelyn are inherently 'good' or 'evil'. In actuality, the Primals themselves are simply running on commands and do what they are told to do. Things get a little more complicated when we consider that they were, at one point, piloted - but as we saw with Elidibus, he and the Convocation simply desired what they saw as best for their people and Zodiark's power did accomplish what it sought to do in regards to healing the Star.

Venat, however, is much more of a wildcard. For her, it ultimately comes down to intention. Was the Sundering an accident or a known result? If it's the former, then she's more morally grey whereas if it's the latter then the water gets much murkier.

I note that the 'billions' of lives supposedly destroyed by the Ascians are swift to be brought up but that came to be as a direct result of the aftermath of the Sundering itself as an effort to restore things to how they once were.

Meanwhile Venat herself admits that her faction are in the minority and that her own people will dislike the outcome - before forcibly ripping loved ones from each other, eliminating their memories and turning them into much weaker beings.

The Sundering also brought about immense inequality. For starters, aether is more prominent in some regions compared to others which means that some nations are given an advantage over others. Furthermore, some races - such as Pureblood Garleans - are unable to manipulate aether altogether bar a few exceptions. We know from side quests in Amaurot's recreation that those with lesser ability to use creation magic were aided by the Ancients themselves. That in itself is a very different approach to how Pureblood Garleans were forced out of fertile lands and into a bleak wasteland, only surviving due to the presence of ceruleum beneath the icy ground.

I don't believe that the Ancients were particularly arrogant or in need of being 'humbled' - that line of reasoning simply appears to be an attempt to try and frame the Sundering as a necessity and a good thing rather than the horrific and traumatic event it was in actuality.

Indeed, we already know that there are other beings in the setting who are immensely powerful as a result of not being Sundered such as Midgardsormr.

In short, it's not a black or white scenario at all at present - and I doubt that will change even as additional information comes to light as Yoshi-P specifically stated that a key theme of the expansion is going to revolve around such.