No matter what Pokemon type I use Aerial Ace on, the damage bar drops really fast, even if it isn't a KO. This happens in both the xy and oras games. Is there a reason for why?
I'm not sure, the only people that truly answer this question with 100% accuracy would be game freak themselves. but here' a short little theory. What if it depends on the animation time? It might sound crazy but the animation of close combat is fairly short, and the hp bar drops insanely fast, and with longer moves (say Flamethrower) takes more time for the battle animation, and the hp bar drops slower.
Source: Personal Experience.
Hope this helps!-Salamaster13