How is dart superior to TS? This is so uninformed. Just like your view of what a type system does.
Dart is very poorly designed, and they managed that even without the constraint of being 100% compatible with good old broken javascript.
It doesn't have null safety. This right here, is enough said and yet we could continue for hours, like how its standard library made the same 20 years old mistakes as java with things like "immutable collections are just mutable collections that throw exceptions", etc, etc.
Flutter might increase the demand and pressure on Dart quality but it's not a good language by any stretch of the imagination.