> C knowledge is still way more generally useful than javascript and/or web knowledge

"Generally useful" is a vague concept. If you judge by number of job openings, you'll probably find JavaScript is more useful. There are probably metrics by which C is more useful.

"Being everywhere" is not necessarily a good measure of the upside one can get by learning it. For example, electronics are also everywhere (more so than C!) but software engineering is generally a better career (measured by income f.i)