I don't think Jack the Ripper needed to be very stealthy. Also note, Astarion has never fed on anyone prior to the game, or so we're led to believe (I don't think he's lying)
I've been assuming that Astarion is still part of the noble scene, and whatever skullduggery he does for Cazador is more the schmoozing variety.
As for playability, if stealth worked a way that having disadvantage really mattered, I could see it being a noob-trap, but as it is, typically either you're never going to make a check, or you're going to fail.
