I'm not advocating for making all (or even most) users spend so much time on internals that they don't get productivity gains. Rather, I'm concerned about maintaining, ensuring generational turnover, and healthily boosting the elite that the product depends on. It is no secret that a number of Emacs ecosystem core devs are middle-aged, and so the project is a few heart attacks or whatever away from losing the experience and competence that has sustained it so well.
Most of emacs is lisp. The actual C part is quite small considering the capabilities of the system. Lisp being what it is, it’s moslty about domain knowledge than language expertise.