Yes, Flutter is Skia + an UI framework written in Dart.

You can also get Skia + whatever you want and get your own "Flutter".

Currently they still have a better experience to sell regarding code reloading, but competing frameworks are upping their game by adding similar capabilities to their developer toolchains.

Yes. More info about why is here: https://flutter.dev/docs/resources/faq#why-did-flutter-choos...

Yes, the Flutter API is a bunch of libraries written in Dart.