Technically the quote belongs to a character in one of Heinlein's novels. He did love writing hyper-competent men though, so chances are he believed it himself

Technically the quote belongs to a character in one of Heinlein's novels. He did love writing hyper-competent men though, so chances are he believed it himself at some point. It's a decent description of a hyper competent person, but I wouldn't say a "deep generalist" in the sense of someone who has prolific knowledge of many different fields of human knowledge.