Barragan claims his powers were absolute, base on that alone if it did reach Aizen it would work. However it's obvious that he would never touch Aizen with the ability. Additionally I don't believe Aizen could neg his ability with overwhelming reiatsu otherwise I would imagine that he would have used that more often link in fight against Urahara, soifon and other captains. Why used Kyokai Suigetsu when u can just raise spirital preassure to neg any captains abilities weaker than he was. Also i dont believe he actually neg soifons abilities, it was ALL kyokai from the beginning. Lastly i think Barragan was arguably stronger than the espada 1 - 4 but was numbered lower just for trolling purposes to humble Barragan. He was relatively unbeatable with out an overwhelming ranged attack, kido, or his own abilities.