Not just air-unblockable, (although it helps plenty) most of the time an AA is a move that deals with people in the air. These moves usually have fast startup to beat slow normals (Ragna 5A), head invulnerable frames so fat normals can't hit the character if spaced improperly (labrys j.B for example just whiffs by narukami 2B deep in if it hits narukami on his invul frames), moves the characters hurtbox down or away from the opponent's attack (sol 5K, a lot of sf AA), have a giant upwards hitbox (or hitboxes, stuff like sho's nonesense lol, aigis 2B) or a combination of these attributes (dps, sol 5K etc.).
The problem with yukari's 2B is that it doesn't do any of these things well. It's slow, so you can't 2B on reaction. It's also not air-unblockable without bomb, so they can return to the ground and you may at risk to play defense. It's hitbox is decent, but not AA status when connected to it's startup. And lastly, its recovery is baaaaad on whiff, so if you miss, yea. Honestly you will be better off J.Aing or jump throw to using yukari's 2B
I hope it wasn't to wierd to read