IQ is a very poor measure of intelligence and mostly shows your aptitude for taking the type of test they give to measure IQ.
If you gave a hundred people an IQ test, and then have the same hundred people come back the next day, drink 350 mL of their 80 proof liquor of choice, and then take another IQ test, would you expect the average of the scores of the second IQ test be different from the average scores of the first test?
I agree that IQ tests are not useful for comparing one person’s intelligence to one other person’s intelligence. I think some limitations of IQ tests can be overcome with good study design or good experiment design. I think they can be used as a benchmark, baseline, or reference for comparing groups of people, or a person’s score before they attended college to a score after graduation. That said, you have to keep the limitations of IQ tests in mind when drawing conclusions based on the data you have collected.