Firstly, it's debatable whether IQ tests measure anything other than how well someone performs on IQ tests. It's possible to improve at IQ tests with practice, and populations overall tend to improve in line with economic development. None of this should be the case for an objective measure of brain "horsepower".
Secondly, one extrapolation that often leads to bad conclusions is pulling inferences from world-class athletes / players etc to make overall broad statements.
The very best chess players are indeed very intelligent with super-human pattern-recognition, visualization and calculation skills. However, it's also the case that chess is 99% about how much you've studied. The guys who believe chess is about intelligence are usually the guys who end up rage quitting because they take losses personally and don't study what they did wrong.
It's only at the very top echelons of the game where the 1% starts to matter because all professional players will have maxed out the study component.
