Flutter is on its way there, too. Already native on iOS, Android, and Fuchsia, with the web build in technical preview and desktop OSes under development.
Even the APIs are not necessarily related anymore. AngularDart is an entirely independent project in every way. I'm a long-time AngularDart dev, and the JS interop thing isn't as important as you'd think. For one thing, it's actually not that hard to do, and for another, you don't need to very often at all, since Dart covers so much of what external JS packages do.
I consider the small hop to TS its greatest disadvantage, personally. JS's ecosystem is a horribly broken mess, and any sane person would welcome a leap to another, better designed one. Dart has JS-interoperability for those times when you just can't get away, but TS is like an anchor holding you down in the mire of the JS world.
Your view seems to be from someone who hasn't used Dart extensively, because no one who had would minimize its advantages this way. Being different from JS is the whole point. Dart introduces all the advantages of TS and more, while leaving the baggage and bullshit of JS behind.
Not just hyperbole, as others have suggested, but most of what you're saying is flat false. Google's (and maybe the world's) most profitable app, AdWords, is built on Angular 2 and Dart, as is their entire internal CMS. Inside and outside of Google, Angular 2's adoption numbers are extremely impressive for a beta framework.
The community is quite active, I think. Most chatting is happening on Slack. Lots of articles/tutorials pop up on Dart Academy (https://dart.academy). For Slack details and other means of hanging with the community, check out the Community Page (https://www.dartlang.org/community).
Dart uses map files for debugging in the browser, but if you use an IDE like JetBrains WebStorm or Eclipse, you can debug right in your editor environment without the provably harmful context switch.
What's really interesting in the comments on this thread is that almost everyone who has tried Dart reports liking or loving the experience. If all those people would push a little harder instead of caving to the status quo, we might just get wide adoption and a great experience for everyone. You know...progress.
I think you would find Dart to be a true joy, given your complaints about JS. I switched to Dart, and now even looking at JS code with all those stacks of indented curly-braces hurts my eyes...
I develop with both, and Dart wins hands-down. ES6/TS adds a lot of Dart's best features to JavaScript, but without getting rid of JS's annoying problems. Many here have mentioned that Dart's standard library is among the best there is, and that's no exaggeration. That alone makes it better.
Whenever I have a choice, I always use Dart. The tools (analyzer, profiler, etc.) automatically make me twice as productive as when I use JS.