How will you convince the Java team to add things you want to make it work better for your framework? You could try adding them yourself but you'd be forking and making your own Java dialect at that point. They did that instead with Dart which they own.
What would you need for a framework that can’t be implemented as a library? Will we recreate every language from scratch for the next logging, gui lib, web framework as well?
For example, making an AOT compiler. Or adding other features. Or making the implementation more suited to client side apps. There are many things you can do to a language to make it easier for a specific use case. In the extreme, this is what DSLs are.
I don't understand why you don't understand that having first class control over a language's development is a useful thing to have.
All else being equal, it is still useful to have control over a language's development. It doesn't matter that Dart may or may not have features not present in other languages, as long as they can add them as necessary based on Flutter's development.
