Citation for for IQ test results == intelligence?
Wikipedia says "In psychology, human intelligence is commonly assessed by IQ scores that are determined by IQ tests. However, there are critics of IQ tests who, while they do not dispute the stability of IQ test scores, or the fact that they predict certain forms of achievement rather effectively, do on the other hand argue that to base a concept of intelligence on IQ test scores alone is to ignore many important aspects of mental ability.
On the other hand, Linda S. Gottfredson (2006) has argued that the results of thousands of studies support the importance of IQ for school and job performance. She says that IQ also predicts or correlates with numerous other life outcomes. In contrast, empirical support for non-g intelligences is lacking or very poor."
https://en.wikipedia.org/wiki/Human_intelligence#Relevance_o...
If we hire people based on IQ scores/things that correlate with IQ scores, we should not be surprised if high IQ leads to better outcomes.
correlation != causation
This ended with https://en.wikipedia.org/wiki/Griggs_v._Duke_Power_Co.. The fact that IQ tests resulted in hiring whites at a higher rate than blacks was deemed a violation of the Civil Rights Act and so the practice was banned. The correlation remains true, but it is illegal to hire based on IQ.
Studies on IQ tests however do control for the factors you named, at least if they are good studies.
Stanford psychologist Lewis Terman’s IQ test, the standard upon which our current tests are based, was meant to show “enormously significant racial differences in general intelligence, differences which cannot be wiped out by any scheme of mental culture.” The Measurement of Intelligence 1016