Wow you don't know what acrobatic means? Damn you must have never seen gymnastic people when they perform plenty of back flips and when they are described as acrobatic people.
Hell read this, its from a dictionary.
One who is skilled in feats of [i]balance and agility in gymnastics.
[/i].
^ Keyword AGILITY which is what the novel has described vader to be several times during his duel.
Or read crimson empire where a flashback shows vader fighting a guy with extreme aglity being to you know, perform kung fu like kicks with a sword acting like a pole(like how neo in the matrix took out his enemies).
And if you can't get your hands on this sources, simply concede your argument that vader is slow as shit, accept the fact that you lost the argument and STOP acting like an idiot.