But that's for individual programs in a larger system. Those of us who live in Emacs do follow the Unix philosophy at the granularity of individual applications inside Emacs or even individual Elisp functions.
This is like saying RIP "do one thing and do it well" because Osm.js has been written for Node.js. Osm.el is a program that does one thing well (view OpenStreetMap) for the Emacs runtime.
"The Unix philosophy is documented by Doug McIlroy in the Bell System Technical Journal from 1978: Make each program do one thing well"