RN does use a lot of native code. It’s not based on a webview like Electron is. Most of the builtin components are native views and there’s no CSS. The JS engine is also simpler. It’s more akin to the lua runtime in Neovim.
It’s a fair assumption. The React part is more about copying JSX and other React concepts (declarative UI etc) but it all boils down to native binaries. The toolchain is also pretty nice. It does hot reloading so you don’t have to recompile the app while building locally. The downside is you get less for free compared to SwiftUI. But SwiftUI also has many footguns and bugs. No free lunch!