There are many people in real life who practice fencing for fun. Most of them (at least most of those around me) also play computer games about fighting. Sword Art Online clearly fits into the fighting genre of computer games. I didn't make a survey, but in any game about fencing it is certainly possible to find someone who likes do the same things in real life.
As I recall, in the world of SAO combos are quick, but very predictable, especially the strong ones, and their speed is not above human limits.
As I assume, if one real-life swordsman would get his hands (or his mind) on SAO, he would wreck everyone. One can move his weapon without combos, losing some speed, but getting a huge advantage of being able to use feints. Plus he would be able to stop his attacks to block enemy's blow, etc.
Yes, he would probably be weaker at the beginning due to not knowing the animations yet and most of combos being very short. Plus, he would probably need to get used to the pace of SAO, which may differ from real-life. But at higher levels he could both identify a combo by it's first "frames", plus quickly react. It would also be nearly impossible to hit him unless he doesn't expect an attack.
One could claim that he would lose muscle memory -- he wouldn't, since this process is more mental rather then some change applied to muscles.
Why did this not happen in the novel, why was it dominated by a bunch of Mary Sue-esque characters? Or did I miss something?