I'm not sure who GJS is but if you see any lisper editing text instead of operating on structures (with auto-balancing parenthesis and so on), it's 99% certain it's in an environment they are not familiar with, so they will make mistakes.

I don't think anyone who write Lisp-like languages professionally doesn't use tools like parinfer/paraedit, where balancing parenthesis is not something you have to do.