Dart feels like an older java in a time when java doesn't even feel like java (with the recent versions, along with other JVM options). For example, try and check out Dart's JSON serialization story[0], it's bad compared to Haskell, Rust and even Go. Dart was rewritten (Dart1 was a train wreck) and Dart2 still doesn't have the features that are expected. Who rewrites a language but doesn't add non-nullable types[1]??
The Dart team is full of smart people, and what they've created is certainly a feat of engineering, but the competition is just tough out there. I consider Typescript to be a better language to write (in this same space, since it's an option for Nativescript), and would consider Swift just barely better, and of course on android you have Kotlin (or Go) as a choice.
At this point I'm generally curious, what do Dart fanboys mark as the strengths of the language over others?
[0]: https://flutter.dev/docs/development/data-and-backend/json