Haven't read every last post in this thread, but has anyone heard of of mentioned the concept of multiple intelligences? The idea that most people are "smart" in at least one way, and maybe smart in several ways, while not necessarily being on the high end in all ways? I think someone who sticks with a reading-heavy, math-heavy, memorization-heavy, visualization-heavy, communication-heavy hobby is probably either good at those tasks or doesn't mind being bad at them (still somehow gets enjoyment out of it). This also explains, to some degree, why people might prefer different styles of gaming -- some people like the number-crunching aspect; some might like minis & a grid to pure visualization, etc. And maybe even explains why some people don't make good DMs. So I guess a definition of "intelligence" very much matters to this sort of discussion, because without it we're probably not talking about the same thing.
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Here are the "kinds of smart" that are theorized under multiple intelligences:
Linguistic intelligence ("word smart")
Logical-mathematical intelligence ("number/reasoning smart")
Spatial intelligence ("picture smart")
Bodily-Kinesthetic intelligence ("body smart")
Musical intelligence ("music smart")
Interpersonal intelligence ("people smart")
Intrapersonal intelligence ("self smart")
Naturalist intelligence ("nature smart")
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Interestingly, I might consider Linguistic, Logical/Mathematical, and Spatial to be tied to D&D "intelligence," while Intrapersonal and maybe Naturalist might be part of Wisdom, and Interpersonal could be something related to Charisma? Interesting to consider.