I beg your pardon? Only a single individual was ever known to have been sacrificed to summon Zodiark: Elidibus, and he was a willing volunteer. The two sacrifices afterwards, also done with volunteers, were for the sake of stopping the apocalypse and restoring life to the world. And the only things we know about the third planned sacrifice is that the Convocation was going to offer up a portion of the life Zodiark restored in order to bring back the aforementioned volunteers. That is a far cry from genocide, and we don't even know if they were going to look for volunteers or not since the whole plan was cut off by Hydaelyn attacking Zodiark.
As for summoning Hydaelyn—not that we even can, since she already exists—I would point to Phoenix, Alexander, the Hard/Extreme versions of the ARR Primals (which actually had story leadups to their summonings, rather than it being holodeck simulation/the WoL thinking themselves half to death), and Shinryu.
Phoenix was a primal accidentally summoned by Louisoix, and whose existence both Alisaie and Alphinaud agreed to omit from their reports on the events of the raid questline. The reason for that was the fear that any number of Eorzeans, still dealing with the damage caused by the 7th Umbral Calamity, would love to summon a primal with Phoenix's power. And as seen with the Alexander raids, they were absolutely right to believe that when two separate groups both attempted to summon Alexander with the intent of using him to create a perfect world—Mide and her beloved (along with their followers) for the good of all, and the Illuminati for themselves. Were it not for Alexander himself calculating that the best possible world was one where he sealed himself away rather than exert his power for anything resembling a good cause, the damage they would've inflicted onto the world would have been a calamity in its own right.
The ARR Primals, meanwhile, had their rematches reveal that the Beastmen summoning them were using living sacrifices to make them more powerful than they would have been with crystals alone. This is carried forward and played for all the drama they could with Titan's reappearance in Heavensward, as Gabu discovered when his own parents were killed for the ritual to summon Titan. And finally, there's Ilberd's plot to summon a primal of his own making—one that would lay waste to everything in its path, including the Eorzaean Alliance and even his own countrymen. He had every single man and woman serving under him slaughtered to empower this summoning, with the only survivors being the two who pulled the trigger. He even killed himself, allowing his own dying rage to take root in the primal's consciousness. This was not, by any stretch of the imagination, the product of "superior humanity" or "evolved spirituality".
So again, I don't understand. Maybe I need to rephrase my question. Why is it that the current generation of humanity has to be better than the Ancients in morality, or spirituality, or creativity, or fertility?