IMO he's safely in the top 20 (out of 41), maybe even top 15 if I were to be generous. At this point I don't think he has any absolutely horrendous match-ups (like Pichu-Sheik in Melee), but Aether isn't nearly as safe as people think once they understand how to punish Ike at his apex and jump-canceled QD as a "gimmick" isn't a big asset if they keep applying pressure. I can see him being difficult for beginners to handle, but at competitive play, he's more "fair" compared to other characters widely regarded to be in the top 10 (Mewtwo, Fox, Falco, Wolf, Lucas, Diddy, Pit, etc.).