I'm not sure I can think of any editor that's as laggy as atom.
In all fairness though: I wouldn't notice 99% of the time, and I can well imagine that this problem will disappear with time.
Emacs' performance can be pretty damn bad sometimes, but I don't use Atom enough to know their relative positions.
I just switched back to emacs from testing atom for a few weeks, and my biggest issue with it was the speed in opening files from a closed client. emacs deals with it by daemonizing emacs-server, atom deals with it by trying to be performant, but failing. In this day and age, i'd rather sink some cheap memory and keep the daemon running.
If atom has a daemon feature that I never found, or one upcoming, I'd consider it again. Until then my workflow involves too many client closes for me to not notice the significant delay that atom has when opening a new file.
I feel like daemonizing Emacs should be the default. I can happily add random stuff to my init.el which causes it to take a little while to cold start, but I never see a cold start so from my perspective Emacs is instantaneous for editing a random file. I keep hundreds of files open at all times and never have an issue with performance. I just go through and prune my open buffers once a month or so, for organizational reasons more than resource usage.
Right now, Atom is just too slow when compared with other editors such as Sublime. Given enough time it shouldn't be an issue (maybe), but right now I think it's a huge pain point for a lot of devs.