Sorry, you might be the author of Backbone, but this is one aspect that you might have gotten wrong. If you had considered it, there would have been more meat in Backbone.

Following your logic, we should all be writing code in assembler or even machine code. Higher levels of abstractions are always good and not everyone ( > 95% of the apps ) needs to fine tune their app to the last processor cycle.

If we are writing an app for a Rocket launcher or some high critical app like that then I would agree that the developer of that app shouldnt be using higher level abstractions / library / frameworks. But these are webapps for gods sake and the computers of today are perfectly capable of handling an average web app and provide 60fps rendering ( unless the developer is seriously stupid ) or in the worst case 30fps atleast (which is smooth enough ). The question is a tradeoff between how much performance you want and how much speed in development you want.

I am sure that for the average developer out there, Marionette or Chaplin will be faster than plain Backbone.