They also use personality tests to screen out job applicants, and that is no argument for their usefulness. I mean you could hire only libras and claim that this policy has given you better candidates, and you would not be wrong. But at the same time you couldn’t claim that libras are better at the job then leos. You have other hiring practices and biases that makes sure you are usually happy with the libras you’ve hired.

An IQ of 100 is defined to be the mean intelligence. It is a magic number (albeit not a magic number representing competence). Usually an IQ of 80-90 (around one standard deviation below the average) give you general competence, lower then that and you probably have some mental disabilities (unless the test is badly standardized; which has happened more often then it should have).

IQs above average correlate with loads of desirable things, individuals with higher then average IQ are generally more well spoken, they have higher income, they are quicker to respond to questions, they know more jokes, they are probably more handsome as well (I know; citation needed). These traits are as well desired (if not more) in the criminal world as anywhere else. But this is precisely the problem with considering high IQs. If your measurement is predicting everything, it usually means you are measuring nothing.