The performance is more than adequate for MVC applications.
It might be slow compared to native applications, especially games, streaming and DSP applications.
But that is where WebAssembly and Emscripten come in to play.
With the improved performance boost that WebAssembly and Emscripten offers,
you can write open APIs that enables your frontend to render in OpenGL, Canvas as well as HTML.
Angular2 is planned to be used as a multi platform front end technology for both hybrid and native apps.
10 years ago there were huge problems with compatibility and stability.
But that is something you can learn pretty quickly.