I think you hit the nail on the head. Slowness in Atom varies so much from person to person probably because it's not in the editor itself, but in the plugins, and everyone has different plugins installed.
Right, that's probably the case. And funnily, the reason why I'm so picky about plugins is that I managed to make both Vim and Sublime Text run horrendously via plugin overload.
Sounds like both should do a better job of telling you which plugins are slowing your system