...ok, tbh TS has a much more powerful and expressive typesystem then Dart, otoh it also works with the constraint of being a superset of JS hence some things are forced to be the way they are since they sit on the foundation they sit.

I don't really like Javascript as a foundation so I'd almost be inclined to throw away a superior type system in order to have the bedrock be something else, opinions might vary though, I know.

And probably we'd all have loved to have Kotlin instead...

Unfortunately the fact that TS is another layer on the top of JS makes the system more error-prone. This was one of the issues I encountered when fiddling with React Native. Too many moving elements in the stack would lead to frequent configuration problems, or the transpilation breaking debugging in weird ways, etc. And once things finally clicked in place, some component was updated, and the vicious circle would start again.