The Flutter webview is basically a wrapper for the native iOS and Android implementations. A native Android app using a webview and a Flutter app running on Android using a webview is using the same native webview.
It is like that for a lot of the Flutter libraries. They basically implement native versions of the functionality and make it available to Flutter. The Dart language has FFI so if you want to get "even more native" you can do Android and iOS system calls in your Flutter app using languages like C, C++, Rust or even Assembly.