Hi again, I can see improvement since the last time you posted. Good job
As for your problems I can spot a few things that might help out.
First off your timeing between frames is a bit long. I put it into gimp and you have a 250ms pause between each frame which is a little long. I reduced it to 100ms per frame and it looks much smoother here is a comparison.


Second it looks you have the right idea with moving the whole body but only horizontally. The vertical movement in the body is just as important.
Third you are also not accounting for 3D movement or movement in the Z axis. What I mean is when you swing a sword you are swinging not just your sword but your whole body as well. Your hips and shoulders rotate as well as your legs. Grab a pencil or a stick and try it out in real life. It makes you feel sort of silly but a lot of high level animators act out their own animations to get a good realization of what they are trying to create.
For myself when I tried this attack I found I twisted my body quite a bit, leaned forward, and bend my front knee a lot.
So as a summary your animation looks a bit flat because of:
-vertical movement
-shoulders
-hips.
-legs.
Here is a realllly rough edit I did, it sort of conveys what I was trying to say.

I hope this helps.