Keep in mind that against air covers both ground-to-air and air-to-air situations. Hazama has terrible air-to-air. His best option here is something like jump back j.b and hope for a CH into super.
Ground-to-air is different though. I find myself mainly using 5a as an AA with Hazama since it hits high, comes out fast, and combos into 5c 4d regardless of counter hit for an easy 2k dmg and meter gain.
214D~B is great because he moves backwards while doing it. When used as AA, it doesn't give the opponent much time to get a good punish (if they can punish it) because of the distance and the time it takes for them to land after blocking. It sucks as a reversal or against grounded opponents though.
6d is a great anticipatory AA at a distance. If you can read when your opponent will airdash, you will land tons of damage. The obvious counter is to simply run in and 5b him, but if you're fighting one of those opponents that likes to jump up and down and airdash right before landing, 6d is one of the best tools at dealing with it while remaining relatively safe if you whiff.
But having good AA options doesn't mean much if you can't make the opponent feel like he has to jump to get in on you. This is his main problem, imo. Threat of random jayoku is the only thing that prevents people from pressuring him endlessly on the ground.