[nearengine]

I think you have a fundamental misunderstanding of RWD somewhere along the line. Your first point is the entire point of mobile-first design. Old and less capable browsers, such as older version of IE don't understand media queries, so they get the "simple" non-media-query, mobile-optimized site and you avoid problems with patching CSS3 queries on browsers which don't support them.

There's absolutely nothing about mobile-first design that makes your site dependent on JavaScript.

Third point depends ENTIRELY on the site, but your logic doesn't really follow. If I only had to pick HTML or CSS, I'd pick HTML. That doesn't mean I'd launch a site with only HTML and no styling. You're creating a false dilemma.