I can't say what is special about human-level intelligence. Most importantly because the scientific community(and by extension me) can't define what human-level intelligence means. It's just too illusive at this point. That something is undefined by humans doesn't mean you can simply say it's not special.
IMHO in the community there aren't any significant objections to the Legg & Hutter definition proposed in that document "Intelligence measures an agent’s ability to achieve goals in a wide range of environments." - perhaps you can tweak the wording some more, but that's the direction implied by people talking about building general intelligence and (at some future point) human-comparable general intelligence; in essence it's about 'wide-coverage' intelligence of being efficient at different purposes and figuring out what is required to be successful for these purposes, as opposed to narrow single-task specific effectiveness; but it's essentially a metric on which one quite reasonably can imagine something being equivalent to or better than the average (or x-th percentile) human.
With that definition you can argue humans aren't intelligent at all. The environments we operate in are very limited compared to for example extremophiles. I doubt anyone would argue extremophiles are of genius level intellect compared to humans. That definition can be falsified in dozens of ways. That doesn't mean it can't be useful of course.
IDK, humans can achieve all kinds of goals not only in temperate climates but also underwater, in the Antarctic and even in outer space; and in the environments where extremophiles operate we can do all kinds of interesting things that they can't.
It's not about the capabilities of unassisted body - I can influence stuff in a volcano without sticking my bare hands in it.
