Sublime (or really any competently-designed native editor) does indeed use way less memory for any text-editing task than any Electron-based app. But memory is fast. VS Code shows that an Electron-based app can exhibit performance basically equivalent to a native app at most tasks (other than opening that initial window, where it's still an order of magnitude slower).
So I think the performance problem with Atom is more Atom than Electron.
(Still, though, if you only have 16GB RAM, you probably don't want to use more than 4 Electron-based apps.)