Emacs uses 'slow" elisp to implement major functionality, but the critical functionality is written in C. Perhaps that approach could be taken with Atom?
And, there have been editors written in a variety of higher level languages for decades, many that are slower than JavaScript, that aren't (as) slow as Atom. There's more to it than language choice.
Disable that, and it runs flawlessly on 10+GB files.
I looked into it a bit a few weeks ago but got distracted. It uses regex and many of the statements could be improved. Plus they use a fairly off the wall regex engine that has pretty poor performance but they use it because it supports every damn encoding under the sun.
I think if that can be figured out, the only "sluggish" part left will be startup (which IMO is acceptable at this point, but improvements would always be welcome)