I came to this conclusion over the weekend. Really wanted to use one of those compile to JS languages, but after doing some interop and looking at their output, you're fighting the browser. Even Clojurescript, which is supposed to have has great code elimination will produce much bigger outputs then regular JS.
One way to look at it is immutable.js minified is 55 KB. That's about 5,000 lines of JS. If you're using a functional language, you've gotta bring along those immutable datastructures somehow, and 5k lines of Clojure is gonna output greater than 5k lines of JS.
Keep a watch for the new Reason standard library, it will bring some stunning reductions in output code size. I mean, right now the output code size is about as minimal as you can get while looking like hand-written JS ... but what's coming might blow all the other immutable libs out of the water thanks to optimisations it can do using static typing information.
One way to look at it is immutable.js minified is 55 KB. That's about 5,000 lines of JS. If you're using a functional language, you've gotta bring along those immutable datastructures somehow, and 5k lines of Clojure is gonna output greater than 5k lines of JS.