By "JavaScript generation", this project appears to mean ClojureScript. Weird way of putting it. That's like shipping a C compiler and billing the feature as, "Assembly code generation".

You can get the ClojureScript runtime much smaller by turning on the Closure (with an S) compiler's optimizations. Still gonna be bigger than vanilla JS, but for that you get a much more expressive language and the ability to share client and server side code.

The debate over whether/when it's appropriate to use CLJS is surely not over. Before judging it as impractical, note that a new iOS weather app written in ClojureScript is getting rave reviews: http://keminglabs.com/blog/angular-cljs-weather-app/