While this provides a useful feature for major-mode inheritance, one
cannot help but question the design decision to extend the elisp
language using ad-hoc inheritance solutions when there are much better
I suspect the people who "cannot help but question" this are a fairly
small. There is no factual basis to claim that people in general, or
even programmers in general, will have this experience.
I installed derived.el because it does the job that actually needs
doing, and was a small amount of work.
Emacs Lisp is powerful enough. Adding OOP to Emacs is not clearly an
improvement; I used OOP when working on the Lisp Machine window
systems, and I disagree with the usual view that it is a superior way
to program. But even supposing that OOP would make Emacs better, it
is lower priority than many other changes (mostly in editing rather
than in Lisp).