It's very difficult for most (not all) people to relate to others who are either significantly more or significantly less intelligent than them. So, for example (using IQ as a proxy), most people of average intelligence (~100IQ) would find it difficult to relate to those of ~65IQ, and equally difficult to find much in common with someone much more intelligent than them (140+IQ). Given power laws / bell-curve distribution, most people on the tails of intelligence distribution will spend most of their time surrounded by people they can't really relate to. This does not seem like a recipe for happiness.

Yes. A useful analogy is to imagine being an adult in a world populated only by children. Aside from the social alienation of it being hard to relate to others, there would be practical matters. The entertainment would all be tedious and predictable, all the rationalizations for bad behavior would be transparently self-interested. Enhanced capabilities for observation, prediction, and planning would make you a super-hero at problem-solving, but really, what does that get you except repetitive unfulfilling effort? Don't sweat the small stuff is good advice, but you couldn't actually ignore the futility. Don't focus on the negative is good advice, but in a world like that pessimism and realism are the same thing. Anyone would be miserable. The good-aligned person would likely withdraw or self-lobotomize. More cynical characters would harden their heart, seize power, and become king of all the blind babies and try to yoke them together and build a pyramid or something. (Yes, I've recently reread Understand by Ted Chiang, No a pyramid is not a plot point per se ;)

Thankfully the situation isn't actually this extreme, but I think what we're talking about is just a difference in degree and not a difference in kind. Seeing more clearly than others seems very uncomfortable at best, and frequently maladaptive and/or a recipe for derangement.

This doesn’t seem obviously true. There’s a bell curve of how knowledgeable people are with tech and somehow people I spend time with end up in the tail end. There’s a bell curve of how much they like board games and I end up spending a lot of time with people at the tail end as well. In general, the people you spend time with are not selected by a process which is even close to random.

I haven't found this to be true. For marriage, sure, pick someone close to you. But I've found that IQ is mostly irrelevant for friendship. Character and compatibility matter more than IQ.

I've noticed that many smart people have never learned how to enjoy spending time in mixed-IQ settings. I feel a bit sorry for smart people who were raised with smart parents and smart siblings and smart friends etc. I find their perspectives very limited.