I think that much of functional intelligence comes from compression and integration of information. That doesn't require someone to learn quickly or think quickly in new circumstances. But it still can result in very useful skills and knowledge that are built up over time.
A lot of this comes from Galenson's research, as mentioned early in the article. He was the thesis advisor for a friend of mine, and seems like an interesting thinker. He wrote a book on this topic: https://www.davidgalenson.com/v1/index.html