Something people have done in the past that may work is that the blur could be part of a different layer, and have individual "pieces" of the effect trail behind the main character and follow their motion. It's a bit hard to explain what exactly I'm getting at, but Joy Mech Fight has the thing I'm talking about, only with body parts. Maybe, "putting it on a different plane," is a better way to phrase it...
Otherwise, I think the legs and dangling arm could have a bit more motion, and not so sudden a stop when the character attacks.