to begin with i started my edit using the old animation you posted, this new one you made improves on that for sure
i reduced frame count of the actual swing and upped the count of the in-between frames, and lowered time between frames (200ms > 100ms), which makes the animation much snappier--makes it more energetic, dynamic, action packed, because the action is quick and he has build-up to the action
on the animation itself, i made the movement more exaggerated (forward more) and added recoil, which is what you naturally do--"recover" from a sudden action (punch and watch your hand--it'll come back a bit). honestly, i should add more forward movement and more obvious recoil, but i'm running short on time, so hopefully you get the gist of it
i also noticed the character wasn't really readable, a lot of detail but i can't tell what it is. i took my best guess and made some changes to the character (most notably lengthening what i assume are arms), especially in colors, which were not very unified and often superflous
finally, i agree with the look-at-a-reference thing. i tried to fit my animation to your funky swing, but really i think it'd be hard to do something like that (i did it myself in front of a mirror, i'm no swordsman but i didn't feel like i could not break my arm doing it haha)
my animation isn't perfect, i don't have much time, but i encourage you to study it and see what i did differently than you