There's a lot wrong with the swinging animation.
Before you animate anything, don't think of "sword swing" think "how does a guy move when he swings the sword?"
remember that the character, not the weapon should be the focus of the movement.
as such i've made the attack more forceful and more like an attack. as it is now, it just sorta looks like he's waving a sword round in front of him. again, just ask yourself how a person would move, not how the weapon would move. the weapon comes rather naturally after that since a sword is *more or less* a simple straight line object.
here's my edit

It's crude because i'm lazy, as usual.
I'm not going to adress any anatomical proportion or style issues because i'm not really in any place to approach them.
Take in mind that attacking something or someone is an action you really have to commit your entire body to do. it doesn't really make sense for any part of him to not be moving while he's swinging. and the body isn't just a set of independent limbs and segments, if you move an arm or a leg, the rest of you is going to move as a consequence. it's all about balance.