I can confirm the experience and I've used dart on multi month projects twice now : first time when it was the JS replacement and using AngularDart back in the angular 2 beta days - it was ahead of the curve at the time with tooling (compared to JS world), but it went nowhere because of poor design choices.

Then they decided to salvage the team and made flutter with it - the technical reasons of chosing it over JS sound extremely unconvincing. And the language is as you say the worst of both worlds - verbose and weak type system (I remember getting runtime type exceptions because compiler couldn't catch a type mismatch in a ternary) and none of JS dynamism, no reflection - just boilerplate on top of boilerplate.

Worst part is the react like architecture of flutter lends itself really well to immutable state management practices but the language is so weak that any immutable library involves a ton of ugly boilerplate - and they refuse to add stuff like records to the language to ameliorate the problem.

The reason it gets me so riled up to rant is that the framework itself and the idea behind it (custom native rendering framework) has potential - but dart makes using it horrible.

Dart is at least adding new features relatively quickly (just recently they started working on immutable record data structures with pattern matching, which even TypeScript doesn't have yet) and soon they'll have static metaprogramming meaning you can have Lisp like macros to create your own syntax, including algebraic data types as in any functional language. That is really what people are looking forward to.

Another thing is Dart is JITed, AOT compiled as well as compiling to JS and WASM. Very few languages can do all 4. JVM ones can't, so no Kotlin (we'll see how well Kotlin Native works), and V8 isn't AOT so no JS or TS either. Only alternative I can think of is Lua.

I think you have made the case for ClojureDart. Clojure does not do the Typescript strong typing thing, but it meets the "Not Dart" requirement pretty well.

And my specific contrib, Matrix, handles state management and the whole reactive thing pretty well, one area where I see a bit of thrashing in the Flutter community. Check out the examples and esp. the TodoMVC demo, they cover quite a bit of ground.