I agree with leffen on this.
More to add: a lot of time that b-air is out, is mostly the weak hit. It's pretty susceptible to CC, or getting straight up beaten. Also, depending on when you hit on the shield it is usually unsafe (the strong part hits high, and if you hit it low you will get the weak hit. So less shield stun).
Oh, and on top of that, b-air has pretty low range compared to a lot of characters' moves, so not only do you usually have to retreat with it but also it can still be punished by some characters even if you are retreating