I keep hearing this, but I never see any evidence for it.

There's only 0.7% Rust code and not even any C++. And almost all of that Rust code is for the CLI, not the editor.

The rest is just plain TypeScript and other web technologies.

Missing the extensions that are required to make a bare bones VSCode actually usable.

Also the performance improvements on the bultin terminal thanks to using WebGL as if it was a native app.