Not sure what you mean by Emacs needing better documentation — IME it is exemplary of particularly good documentation + introspection, integrated well with the editor.
I agree that emacs comes with almost all you need to understand it, but there's one inherent flaw: it's large. It's a joke in the community that nobody is immune to a late "wait, emacs can do that ? I've been using it for N decades and I had no idea.."
One thing that I wondered is how to make the manual more lispy/repl oriented.