Expo Modules Core is the only module that is bundled in. It is a small runtime library that defines the Expo Modules API used by other modules, and adds about 150 KB to a production build of an app downloaded from the stores. A hello world iOS app made with Expo ended up being smaller than the same hello world app that used RN without Expo due to the Xcode settings.

There are also no custom UI controls or animation libraries bundled with Expo. The Expo Go starter app includes a preset SDK, and when developers create a build for the app stores or a development build of their own app, only the libraries they use are included.

IMO it would be a meaningful improvement for the react-native package to provide the minimal runtime needed, namely JSI, Hermes, Turbo Modules, Yoga, Fabric, and perhaps a few primitive view components like View, ScrollView, and Text. The package provides more than a library needs. Animations and gestures today are better served in my experience by modules outside of the react-native package, like Reanimated and Gesture Handler that use truly native gestures. React Navigation uses the system navigator UI and Expo Router adds file-based routing and universal links. Expo Image adds support for modern image formats like AVIF and WebP and uses mature, performant image libraries like Glide and SDWebImage. So there is definitely still work to be done that can improve quality and reduce complexity in RN.