As I've said many times, Watson being able to come up with correct responses that often is impressive. Watson winning Jeopardy! is what's not impressive.
I would be interesting to know how the human contestants would play on their own. We only see them in competitive matches, so we don’t really know how many of the questions they would and could answer. (I heard that contestants tend to push their buzzer as soon as they hear one of their competitors pushing the buzzer regardless of whether they know the answer, so you can’t even know from buzzer presses alone whether the would answer if there were no competitors.)
84% is, to my mind, very high. I’m skeptical of claims that even the best humans are better than that.
