An important architectural point that is missing from this summary: Flutter’s widgets are not OEM widgets. They are a native representation of those widgets rebuilt with a combination of C++ and Dart. This differs from pretty much every other cross platform approach (React Native, NativeScript, etc).
This has both positive and negative connotations. On the plus side, these widgets are built with performance and developer ergonomics in mind. On the negative side, there are quite a few widgets that are under development. Writing a flutter widget is also not as simple as just wrapping flutter around an OEM widget, especially if you don’t want to render it standalone.