Regardless of their lack of depth, we still don't know the whole story, and until we do we can't say following Hydaelyn's will is the best course of action. We still don't know the whole truth, and until we do we can't just write off the Ascians as one-note cliché villains intent on spreading death and destruction for shits and giggles (or to resurrect Zodiark).
According to the Word, this is because Zodiark began to covet power which upset the balance, leading to His banishment. That said, this is only half of the story, and until we have the other we can't decide what the truth is... or at least, what truth we want to believe in.
Am I saying Hydaelyn is evil and we should go deicide on Her? No.
Am I saying the Ascians are just misunderstood and we should consider joining them or leaving them to their devices? No.
But we at least deserve to know why we're fighting beyond "to keep the Darkness banished" and whether or not, for everything we have done and all the people that have sacrificed themselves, it's making any tangible difference.