I didn't write all of the Emacs Lisp programs I mentioned, but I did go through most of them, changing the way they work to fit how I wanted to use them. This was an iterative process that is still ongoing.
What should impress you is not the breadth, but the paradigm itself as expressed in Lisp. You can probably write an IRC client in JavaScript and have it in VSCode. But that's not what I'm talking about. We're not ticking boxes down a feature list here to say "JavaScript can do that!". We're talking about a paradigm, and specifically about interactive development with a short feedback loop through Lisp which is "a difference that makes a difference" [2]. But in order to truly understand this, you have to go through the process. Philosophical truths can not be transmitted like pieces of eight.
[1] https://www.dreamsongs.com/WorseIsBetter.html
[2] http://www.informationphilosopher.com/solutions/scientists/b...
Extensibility was emacs' killer feature when its main competition was vim and vimscript - that's just not the situation anymore.