IQ is good as an indicator, not a predictor. You can make assumptions that will likely be true on the basis of IQ, but there's very little that you can say for an absolute fact on that basis.
When IQ is indicative but not predictive, I just don't see much use there. If I can't predict future behavior, success, or some other metric then I'm not sure why I'd zero in in IQ specifically. I have also found past experience to be indicitive but not predictive, and I don't need to trust a standardized testing method to review experience.
Even though on paper I may be high-potential, in real life I'd prefer to be normal, and for every one of me that exists, there's a 100 IQ person who has the drive and willpower to achieve things that would be considered atypical. Both of us are exceptions, but we both still exist.