Well Emacs is faster to me because its just a lisp interpreter written in C, tightly close to the hardware. So yes, Emacs is like 80% Elisp, but it still runs fast, and its stable. Editors like Atom are a bit too... "abstract" maybe. If I understand, Atom is CoffeeScript/JS running on a the Electron shell which runs on NodeJS which is written in C++ IIRC. Thats at least 3 levels of abstraction in my point of view, and knowing that Electron is Chrome based, it can't improve its speed. Simpler is faster
It still somehow manages to feel faster than many other editors.