This is exactly how I feel. The lack of freedom to choose your own language is appalling. I don't want to be locked into a single language. If they targeted the JVM platform instead, would have the choice of Clojure, Scala, Kotlin, JRuby, etc. Also, targeting the JVM makes a lot of sense of Android, since ART complies JVM bytecode down to super-efficient machine code (at installation). I was really disappointed by Google's decision to push those wanting to use Flutter to learn Dart. Fortunately, the Flutter Windows and Linux libraries provide C and C++ wrappers[1]; hopefully these become preeminent, and result in other language bindings for Flutter. I've been tired enough with the web being JavaScript-dominated for a long time that the rise of options like TypeScript, ReasonML, Elm, etc. (in industry) felt like a breath of fresh air to me.
WASM would be a much more suitable platform for Flutter since it's more portable (works on the web) and better matches Flutter internals (C++ can be compiled to LLVM and through that to WASM).
Not to mention that Google might be a bit sensitive to anything JVM / Oracle right now, given the lawsuit they lost.
[1] https://github.com/flutter/flutter/wiki/Desktop-shells#c-wra...