VS Code wasn’t based on Atom. It was written from scratch. The system architecture is very different.
VS Code uses Electron, but all the heavy stuff is running in separate threads or processes, which is why it feels faster than some other Electron apps.
Unfortunately, many Electron apps break the #1 rule of desktop app development: Never do any heavy processing on the UI thread. Any Electron app that does heavy-ish processing really needs to use node:worker_threads or something similar, plus a UI library like React that can prioritise handling of user actions over rendering other parts of the UI.