I'm wondering how did AZ turned his machine into the ultimate weapon after reviving his Floette? HOW did he sacrifice lots of Pokémon in order to restore his Floette, thereby ending the war? I think the reason why Light of Ruin's effect causes recoil damage to the user a lot is since Floette was upset that AZ took the lives of Pokemon to not only bring it back to life, but once again to end the war, all because it died in battle. Understandably, Floette felt AZ had taken things too far, that its death changed him for the worst, out of shame for itself and disgust for AZ's actions it left him.
Yveltal and Xerneas were simply a power source Team Flare was using to power the machine, they have nothing to do with AZ's story. So I was really thinking Zygarde may have a part in this during the war, and it came from Perfect Zygarde's power that AZ was able to revive his Floette, and end the war with the huge blast