VSCode has hardly any functionality a modern IDE has unless you had dozens of extensions and then it slows down
Where is the slowness?
The post is about UI being in native for performance reasons, yet most of the processing/heavy logic of an IDE already is, or in a separate thread, even if the UI is in Electron.
At which point you're just discussing the performance gap between Canvas rendering and native graphics, which to a large extent disappears with WebGPU.