I think one flaw in your analysis is that Flutter is not analogous to "Java in the enterprise": it's already very pleasant to use compared with modern web frameworks.
Java 11 is pretty sweet, and the JEPs roadmap is enticing.
Meanwhile Dart has adopted all the features I dislike in Java, like @Override instead of proper keyword, virtual methods by default, no value types and so forth.
Maybe by Android ZuchiniBread we'll be able to use Java 11 on Android.
One of the major pain points of Android development is that the vast majority of the API is designed around limitations of Java 6. Yes, I know that you can use most of Java 8 for Android now, and Kotlin is pretty good. However, it took far too long for Google to deliver that to developers.
Meanwhile Dart has adopted all the features I dislike in Java, like @Override instead of proper keyword, virtual methods by default, no value types and so forth.