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.
Nonetheless , the API seem to be behind the original. Hence interop with JavaScript seems incredibly messy and time consuming.