Do you really think that Link played the same as he does in Zelda? Or that Ezio played the same as he does in Asasssin's Creed? Or that Geralt plays the same as he does in the Witcher series?
And outside of Namco games, did you know that Capcom put Mega Man in a fighting game once? I mean, how could they have done that, right? He definitely didn't play anything like what he did in Mega Mans 1-6. Fans must have hated it, right? This was twenty years ago, and I'm sure Capcom learned from their mistake. They must have realized that characters from games of totally different genres (such as Resident Evil, Final Fight, Devil May Cry, Viewtiful Joe, Bionic Commando, Okami, Phoenix Wright, Monster Hunter, Dead Rising or Ghosts 'n Goblins) would just never work in a fighting game.
For real though, taking a character from another genre and adding them to a fighting is an adaptation. Most people understand this. A talented team (and I think SoulCalibur VI has a good one) can take elements from the original character and adapt those elements to make them work in their own game. I'm not saying it's going to be 2B or anything, but it's absurd to argue that it can't be done.