IMO any "old enough" and complex enough software suffer some kind of "age&complexity" problems... No matter how you design it, unix choose simplicity and we see that today no real unix exists anymore (yes, they do exists per name, but in fact they do not follow unix principles), ITS, Emacs, LispM, Alto, ... choose integration and completeness and except Emacs they are essentially dead... Modern software try to choose…
if you read emacs/lisp mailing list, people were already crying about the vast difference in capabilities, ergonomics, ease of use.. saying that emacs was really really below what lisp machines editor would offer. Not even talking about the near fully reflective OS. Can't find the newsgroup url yet. But still it seems that we are far from peak even 30 years after these systems died. There's a smalltalk/pharo mooc onl…
However, for a rare circumstance my first computer was a decommissioned SGI O₂ donated by family friend so I have the privilege of having use SGI CDE as my first desktop environment and growing up I see how much we lost, even in PC case vs what I call "normal" well designed case with easy access and proper components and cables pass layout...