@whynot: They might have a higher “G”, or general intelligence, but have a lower spacial or linguistic intelligence. Or maybe the other way around.
Also, you can’t judge an individual based on a group average. For example, Haiti has an average IQ of 67. Yet, if a Haitian were standing in front of you, you can’t say he has an IQ of 67. That would be incorrect, and he might be the smartest guy in the world. You also can’t take an intelligent individual and attempt to invalidate a group average.
“I know Mr. x. He’s a Haitian and has an IQ of 130, so your statistic is bunk.” - that sort of thing.
And you are correct that in individual cases low IQ people can be successful - but probably not at something like a medical doctor. But that person might have a special/valuable talent.