Consider a weightlifting competition where the weight-limit were 20lbs (10-kilograms). You'd be able to determine those with severe injuries or deficiencies vs a typical human, but you wouldn't be able to determine a peak-athlete from an average person.
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Now sure, we can increase the reps to absurd levels, like "200 reps of 20lbs", which will start to separate out the athletes from the typical humans. And that's roughly what the upper-end of the IQ test does: you need to be more-and-more accurate / fewer mistakes to reach 115, 120, 125 IQ or above. But we've have pushed the test far beyond its intended purpose.
IQ itself partially depends on a somewhat unproven concept of "general intelligence", which IIRC no one is even sure if it applies to average (or smarter) humans.