Yes, I get that, but because they're both based on Electron, they're essentially both browsers and will do all their rendering through DOM manipulation. Yet VS Code is reported to be much better at it than Atom, so I was wondering what architectural differences account for this.

It seems there's some dramatic differences in how plugins are integrated, meaning some things are easier/harder to do via plugin. The VS Code UI is much more fixed than Atom as well... that said, other than getting used to the open files on the upper corner instead of tabs, it hasn't been bad at all. It's just out of the way enough.