Atom is nice, but it is an Electron app, meaning it is a web app built in HTML/CSS/JavaScript with a desktop wrapper around it. Electron apps can be notoriously resource intensive.
Atom shares a lot of DNA with Sublime Text, which I find to be more respectful of resources (but otherwise very similar, if perhaps a bit rougher in some ways).
It’s possible to create syntax packages that are simultaneously compatible with both editors.