We accept the basic idea that musical skill is multifaceted, and anyone who would try to assign a single number, or even two numbers to musical skill would be laughed at. The same is true of athleticism. We intuitively understand that there is a difference between being strong, being quick, be agile, having exceptional balance, etc. But the idea that “smart” comes in different flavors (linguistics, math, spacial, social, etc.) eludes us.
Tom Brady may be the best quarterback to ever play the game, but he was a six round draft pick. If the NFL draft had been an IQ test, with no other entry criteria, Tom Brady would never have played a down of professional football.
The roots of IQ are rooted in racist outlooks, and were used to defend racist policies. Originally, the argument was that skull sizes dictated intelligence. Because blacks had smaller skulls (on average) than whites, made them more stupid. The fact that black males had larger skulls than white females was discarded from the analysis, since it did not support the preconceived “conclusion”.
Today, the theory has multiple policy implications, in that conservative Republicans are always trying to cut training programs to help the poor, since, after all, the poor are poor because they are “stupid”. And “stupid” is incurable, since it is supposedly rooted in genetics.