>If measuring something like the visual reaction time of people makes sense, then so too does measuring IQ.

I don't know what you mean by "make sense". To me it doesn't make sense insofar as it purports to put a single number on a very complex concept that no one really knows how to define or agree on a single definition. The traditional "predictor of life outcomes" motte-and-baley fallback isn't satisfactory for most people as it relies on circularity (in our society much of our life outcomes is actually determined by how well we do at tests that are strangely similar to IQ tests) and fails to account for the many, many socially maladapted yet gifted people out there. It's also unsatisfactory as it pretends to capture something from the inner person but outsources its definition to the outer world.

Also, none of that explains how one's IQ test results may predict one's ability to appreciate 'sophisticated music', nor is it clear what is meant by 'sophisticated'.

When has anyone ever claimed that being socially adept correlated with IQ? It's long been a trope that geniuses were eccentric and socially mal-adjusted. Even Isaac Newton, centuries ago, was known to be an odd recluse.