But similarly, he might well know these things to an above-average level, and just think that he doesn't.
In a practical sense that should be fine, given the level of specialization that a company like Facebook can have given its size and scope. But I wonder if Dan would make it through the average Facebook engineer interview without his Redux cred however.
He is also the rare person who is very honest about this kind of thing which is refreshing. For example he claims he only vaguely understands time complexity ("nested loops are bad").
I don't know exactly what point I'm making here, besides there can be a disconnect between a developer interview process and what people actually contribute. I think engineers should strive to be solid at the fundamentals, but at the same time there are very productive people who just learn as they go. Also, it takes a village so to speak, and over-optimizing for Comp Sci majors who drill LeetCode may not be the best long term choice for building teams either.
I am talking about people like Jon Gjengset who got hired to work on Rust at AWS.