Really? Backbone collection/models are a simple layer with an Ajax call behind. No relations, no lazy loading, etc. Backbone models are akin to an ember object with a fetch/save call, nothing more. (Good for some scenarios, but not enough for "ambitious web app" IMO)
Ember data has a bigger goal than this and, yes, it takes time to get it right.
The "run loop" hooks into the existing browser's event loop in order to coalesce side-effects. This is exactly the same thing that the browser does when you make a number of changes to the DOM in an event handler.
You can turn that off if you want, personally I don't miss much of it.
As for the even driven stuff. Not sure what you mean by that, the run loop is not to dispatch dom events but to settle the bindings asynchronously (with the benefits of not triggering multiple changes for the same property within the same run loop and having a comprehensive pipeline to get data on the screen).