Miss Meta Mon
I ♥ Poké Dolls
TBH, I don't think they thought that much about it. Mega Evolution to start with was specifically said to be a Kalos Region phenomenon, both in-game by Sycamore and on the official site. The new ORAS lore is kind of a retcon. Unless we run with Zinnia's multiverse shenanigans, but I feel like that would undermine the Regions being tied together...
I think they did a better job with the Devon history.
You're forgetting though, that AZ is a part of the Omega Ruby / Alpha Sapphire canon. He is mentioned by Wallace as he (Wallace) is talking to the old man in Sootopolis.