There could be a time period in which cognitively well performing people are rewarded much better than in the past, so all the predictions of highly cognitive people will seem pessimistic on average, compared to others.

So for example, let's say tech starts to boom, and everyone good with tech will all of sudden have much better financial performance, although everyone were making their predictions based on historical performance.

It matters because if specific hard-to-predict one-off events hadn’t happened (e.g the Brexit vote), the optimists might have come out looking much better.

Because the results also depend on the economy. Different times might provide more wealth to people in different strata.