Writing code by hand isn't too bad, especially with a good language like LISP. I don't think it requires too much extra effort, just more attention and care as to not make syntax mistakes. With near-instant compile times and auto-linting, we sort of lose the ability to auto-vet code before inputting it.

The scope is much more limited in his case. When the problem space is super narrow and the base language is your whole environment, writing correct code in a big batch is not that hard. On the other hand, dealing with flask and basically the whole stack of everything web at the same time is a different kind of challenge.