The humans were not within the current normal range. The average was explicitly higher. And I think that the aliens average intelligent was lower than the current human average, although the story is not explicit on that point. And there were billions of super-humans.

Let me put it this way: Google is smarter, wealthier, and more knowledgeable than I. But even if everyone at Google thought millions of times faster than everyone else, I still wouldn't worry about them taking over the world. Unless nobody else important knew about this capacity.

AI is a serious risk, but let's not underestimate how hard it is to be as capable as a Straumli Perversion.