What's I think people are missing the most about difference between Atom and VS Code is the UI.

I think it's the main difference between them. Atom was about creating a Sublime text with web technology, it's just a text editor, you open it and you can write code, it's very easy to use.

VSCode was more about creating a IDE with web technology, so the UI is a lot different and a lot harder to use for someone just starting to write code.

Performance wise Atom improve a lot during the last year and I don't see any difference in performance between them on linux.