Precedents That Aren't
There's a minor problem with the above analysis. Humans aren't obsolete in chess. A human–machine combination can beat both unaided humans and unaided machines. There are even Advanced-Chess tournaments, in which the players are human–machine teams.
IBM's Deep Blue beat the world chess champion in 1997. In that narrow field, by that narrow definition, a Singularity happened then. No big deal. We could comfort ourselves that a computer could never beat us in a contest of general knowledge.
Either way, something important just happened... another Singularity like 1997, but of much greater consequence. It's rare that I need chess advice. But general knowledge advice? I could use that constantly.
There is a problem with an analogous Advanced Jeopardy. Jeopardy, as presently played, requires fast reactions … one reason Watson won. I suspect a human–machine combination would have even slower reaction times than humans. On the other hand, this can be fixed:
Indeed a totally fair contest would not have buzzing in time competition at all, and just allow all players who buzz in to answer an get or lose points based on their answer. (Answers would need to be in parallel.)
Addendum: Futurisms has more reasons Deep Blue was not a precedent for Watson.