Probability noted, and post edited.
I agree they would be more powerful in some regards, living so long, and having time to build up an array of skills, but do we actually see that much of the day to day life of an 'avereage' Tiste Andii. I'd assume that not all of them are soldiers and mercenaries, and even then, I wouldn't be inclined to assume they all practice magic, unless the source material says so.
I'm trying to go for balance as a Player Character. I see nothing wrong with making more powerful ones as NPCs, be it as opponents, or whatever use they may provide to a game.
@ Da Boss
Your comment on size has been noted and included.
That's what I reckon to, its more down to skills and time then their stats, and magic too. I know they are Children of Darkness, but I remember some other vagure reference somewhere about a connection between them and Chaos. I could be totally wrong on the other hand.
I agree with Soletaken, but would they make a suitable player character race with such abilities?
This thread also raises some interesting points: