You can find Deoxys at the top of Sky pillar after beating the E4 again, I believe, Liriia.

Working on my pokedex right now myself. I don't really do much competitive stuff.

EDIT: Also, just to comment on you not putting legendaries on your team, you have to put some legendaries on your team if you want to catch some of the Legends in ORAS. Like having the three lake pokemon in your team to catch Dialga/Palkia.