I'm going to respectfully put my two cents out there, but no one has to necessarily listen.

While it is confirmed that Arceus is the creator of many--if not all--of the Legendary Pokemon of Sinnoh, as well as creator of the landmasses of Sinnoh and Ransei, and is confirmed to definitely be one of the most powerful Pokemon, it is not the altogether "God" of the Pokemon World. Mew still gave birth to it, just like it did nearly every other Pokemon, save those created by Arceus and mankind. If it truly were "God", then it would not have been surpassed by Rayquaza and Mewtwo's Mega forms, which it invariably was.