@Abnormal: I definitely see what you guys are trying to say, I just don't think it's entirely correct.
You're right in that usefulness is situational. But the number of situations in this game is finite. So, this is a variable that can be measured. If
Karen is better than
Robb Cr in 3,487 different situations, and Robb is better than
Karen in 2,765 different situations, we can safely say that
Karen is the better card, right? A concrete answer does exist.
Granted, none of us have the time or the energy to do anything like that. Fortunately, many situations in UR are comparable. By speculating about these situations, we can often make an accurate educated guess.
I actually went on to start listing Robb and Karen's advantages and disadvantages, and trying to explain their impact in the current meta, but that little article goes well over 1500 characters... So I'll skip it (unless someone particularly wants to see it.) The point is that we can make a very good educated guess based on how strong SoA is in the meta, and the introduction of many cards with great round-winning ability to the game (meaning that
All Stars don't necessarily get a huge edge in a 3-round-win strategy any more just because they drew Robb.) What's more,
Saki serves a similar role to Robb while providing much more flexibility.
So the educated guess is that
Karen is overall better, and IMO that's a valuable piece of information -- even though there is no 100% proof.