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.