Every vim/tmux user has created an ad hoc, informally-specified, bug-ridden, admittedly probably quite fast implementation of half of Emacs.
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Maybe you have no idea how much Elisp code is out there in the wild. There is a LOT of things written in Emacs Lisp. Elisp is probably the most widely used Lisp, with the global total codebase amount exceeding both Clojure and Common Lisp combined.
There are things built into Emacs that some specialized apps don't even have. Did you know that Emacs has built-in lunar and solar calendars, for example?
Just by comparing the sheer amount of code, of course vim+tmux may feel less complicated - they give you fewer opportunities to encounter complexity because they offer significantly less functionality out of the box.
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