Is it truly demanding a sacrifice from the planet when the life brought forth by Zodiark wasn't even entirely a product of it to begin with? The Ancients sacrificed themselves to create Zodiark and later did it again to restore life to the world, meaning they did not need to utilize the planet's reserves of aether for the act in the first place. Thus, any life brought forth by Zodiark is, in my opinion, already removed from the natural order. Sacrificing this life to bring back the people that died to give Zodiark life just seems reasonable, and it in no way would harm the star. If anything, restoring the Ancient population would have been a great boon given their desire to resume living for the planet as they had.