Well, it's not even an aerial one that's the problem.
It's just the command grab being an option that makes it a threat.
Let's say you block a 5A. Bam, you're stuck in a 50/50 right off the bat. Now you are going to have to start guessing and going for up+back, which is going to get you combo'd half the time. A lot of the time you will eat more damage just trying to avoid the grab than the grab actually does.
In Haku's case his counters are an extra layer of defense that makes him harder to crack, but the command grabs shut that down, and force you to play into their game.
For characters with DPs like Ragna and Jin it's not as much of an issue, because Inferno Divider will body a command grab just as well as a normal attack. But for counters you have to make a choice.