I actually see the Google-backed web technologies as a net negative. The general pattern is that 1) the community starts to develop good tools that work well in all browsers 2) Google comes along with a technologically inferior solution that they developed in-house. They present it as being ostensibly completely free and open source, but it is designed in a way that means it will be faster in Chrome and hard for other browsers to support as well due to different architectural decisions. 3) Google markets the solution well through its large and well connected employee and fan base, and so the Google technology gets much more adoption than the earlier and technically better alternative. Presumably they do all this in an attempt to make the web unusable through any browser except Chrome, so they can over the long term replace the open web with the 'Google web' that they control.

For example, compare Ember and Angular; Ember's architecture records the dependencies between values, and only updates what needs to be updated when an upstream dependency changes, while Angular has to recompute everything on every 'digest' cycle. When it comes to writing directives in a complex Angular application, you often to set a numerical priority field to the just the right number to get things to happen in proper order - leading to spaghetti code that is hard to reason about and fragile to extend.

I think Dart is even worse when compared to better emerging options like ghcjs (which compiles Haskell to JavaScript) and Elm; these alternatives have more powerful type systems that make common patterns like reactive programming and generic programming much easier and safer. Control structures that are built into Dart (e.g. the 'async' feature) can be treated as just one instance of a general type class (e.g. Monad) with ghcjs.

I think everything considered, these highly promoted and usually highly adopted but technically inferior Google front-end technologies are actually a net negative for the web.