It does set your variables as immutable, just not your values. It makes sense if you see variables in these languages for what they are: references to values.
This has nothing to do with MVC, ABC, <put your architecture here>. You should eliminate the initial browser blank state, optimise the TTFB and your start render time, number of resources <23+4 Steve Sauders optimisation techniques>.
Twitter found Time To First Tweet as an important KPI, and it caused them to build a mixed deliver architecture (server-side and client-side, http://engineering.twitter.com/2012/05/improving-performance...)