Comparing framework size directly is not very meaningful. For example Bustle.com, already running Ember 2.0 today, sits at:

  * 155K of vendor JS (Ember, jQuery, addons)
  * 76K of app JS

Artsy.net is a universal/isomorphic JS website using Backbone. Backbone is maybe a tenth the size of Ember, maybe. Their homepage payload sits at:

  * 26K jQuery
  * 6K raven JS
  * 127K analytics JS
  * 300K main layout JS
  * 274K homepage app JS
  * + stripe

Now I also think Artsy does a lot more than Bustle, to be fair. However the point is that framework size is only a part of the story. The complexity of your code, how you ship it, and how concisely the framework lets you express a design are all extremely impactful.

Ember gives you a big bang for your buck with that 108K (a minified, gzipped 2.0). In practice not many people find this to be the main performance hurdle in their apps, but regardless we're working toward smaller payloads (something we call "svelte builds") and better initial execution performance (https://github.com/emberjs/ember.js/pull/11576).