The Gen 4 legends were the creatores of the world.
I assume the gen 6 legends are gonna be the care takers of the world, one in charge of the living and one in charge of the dead?
Eastern myths people, eastern myths.
This follow the structure of Eastern myths. Arceus might have created the world, but that doesn't mean It governs it. That's why it birthed Palkia and Dialga. It's why you have various gods managing certain domains.
They better have a cut-scene where Xerneas is walking and has plants growing underneath his foot after every step.
Also they should have Yveltal do the exact opposite. Everything he flies over dies and decays. So basically the Forest Spirit from Mononoke split into a deer form and a bird form rather than a giant figure made of some fluid.
They could also add in some kind of message about how destruction takes but a moment to spread while life takes time to regrow. Then again pokemon has always had an awful story so even if they did something like that then it would be done wrong.