Someone who does well on an IQ test but never achieves anything may have been lucky on the day he took the IQ test and never have been that smart to begin with. He also may have had bad luck later on. Few people would find objectionable the related idea that someone who did poorly on an IQ test but later did brilliant work had his IQ understated by the test.
I think you have an oversimplified view of talent. Talent and the ability to achieve (in school or elsewhere) are far, far more than IQ. There are the factors Dude pointed out, but there are also personal goals, ability to get stuff done/sedulousness, and ability to fit in with others in a work environment who think very, very differently from the HG+ person.
Plus, while anyone with a high IQ can bomb an IQ test with ease, it's effectively impossible for someone with a lower IQ to get "lucky" and be able to remember 12 digits written at the end of 12 paragraphs that had to be read out loud, or draw the next pattern in a series of complex patterns, or get the analogy right if he doesn't know what the words mean. He might lucky on a couple questions,
but not 30. 
