Urm, I take it you've never read a single Witcher book or something about the lore? They've actually used the very same swordsman for motion capture like in TW1. The reason his fighting style is so "swinging" and dancery/spinny is because a lot of the monsters that witchers fight are too strong to parry with any weapon or counter, or employ unconventional fighting methods (wraiths being ethereal for example). Most of the time witchers have to dodge attacks or wrap around enemies using pirouettes because of this. This is why their fighting style is more like a dance than anything else. Think of it this way, witchers are the equivalent of jedi. The light saber need only touch the opponent in order to do do damage and therefore maximizing agility and dexterity in your fighting style is more important. The silver sword need only touch the 'flesh' of magical creatures in the witcher world in order to do damage, and so witchers fight in a dexterous extravagant manner similar to the jedi. Witchers try not to fight humans which is why this style of fighting is very risky and might look odd to people outside the witcher combat expertise but witcher senses and reflexes allow them to time attacks so precisely that they can afford to put all their momentum into a spinning attack. The actual reason for the spinning attacks etc. itself is because witchers usually only strike after a successful pirouette dodge (The book Blood of Elves describes this in detail). If anything, the way Geralt fights in TW2 and TW3 is actually much more faithul to the original source (the Witcher saga books). It's really supposed to be like that, which is why you see the key difference between how normal soldiers/guards fight and when you or other Witchers battle.