You know what I think?? I think that this myth that Arceus was the one that created the universe, is some kind of legend that they are letting us know what the people of each Region think of their own legendary pokemon.
My Point:
*The majority of people think and believe that GOD created the Universe.
*In other Countries there are Believes that Izanagi and Izanami created the universe, Zeus, Chaos who was the original state of existence from which the first gods appeared, An from the Sumerian pantheon, Janus, Amaterasu, and I can continue on and on, and all of them created or had something to do with the creation of the universe, but I have one question. Who of these Gods is the real one? Which one of this countries is right?
* They could just like that in generation VI (if there is any) create another "God of pokemon" based on the legends of the ??? region, and on Generation VIII bring another one according to the legend of the ??? region.
*For me Arceus is not the God of all pokemon but one of many, and they could be appearing one by one every two or three generations.
*By the way all of Arceus's legends of it creating the universe are just that, legends, with Ho-Oh that doesn't happen cause we have the crystal bells and the Burned Tower, Groudon and Kyogre we have the Blue and Red orb, and so on.
*And we have what? the Sphere of Life? that doesn't prove that Arceus created the universe, and because Arceus can change type by the use of the plates, so we could say that Mew is the God of all pokemon, because Mew unlike Arceus has in its DNA and can transform into the 16 types, so for me that's not a prove but a legend.