that you know a group of people who are good at predicting and habitually disagree with them.

It seems to me that this is exactly the sort of thing that can really happen in politics. Suppose you have two political parties, the Greens and the Blues, and that for historical reasons it happens that the Greens have adopted some ways of thinking that actually work well, and the Blues make it their practice to disagree with everything distinctive that the Greens say.

(And it could easily happen that there are more Blues than Greens, in which case you'd get lots of systematically bad predictors.)

Sorry, I should have said "worse than random".

We are in complete agreement, and I should have been explicit and said I was refining a detail on an approximately valid point!

It seems like there should be far less such people than there are legitimate good predictors.

And it seems like those that do exist should have less money to be betting on markets! If not then it would seem like the other group is making some darn poor strategic predictions regarding the rest of their life choices!

It's easy to lose to an efficient market if you're not playing the efficient market's games.

Yes, like it is easy for a thief to get all my jewelry if I break into his house and put it on the table. Which I suppose is the sort of thing they do on Burn Notice to frame the bad guys for crimes. Which makes me wonder if it would be possible to frame someone for, say, insider trading or industrial espionage by losing money to someone such that their windfall is suspicious.