Dunno why, but yeah this is pretty bad because if the opponent crossup, flash will hit at the wrong side lol. And a perfect vertical jump in will screw him. Also, it's 12 frames (BA and aquaman is 7).
The only good shit about his d2 is a smaller hitbox. Flash can get Under HG's mace charge using so for example.
But nevermind, I like the fact that a character can have some weaknesses (achila).