Nop, but if you want to be fair jQuery's addClass is also not implemented in those 29 lines of code, it also uses these: each, jQuery.isFunction, getClass and stripAndCollapse.

Umbrella's single eacharg() uses in exchange .each() (which is public-facing, so it really doesn't count) and .args(), which is private but used in MANY places through the code. At 11 lines for args(), I'd say proportionally it'd be 1-3 lines corresponding to addClass. So worst-case scenario it'd be the equivalent to 8 lines exclusive for a much more flexible function with no internal dependencies which is still alot less than jQuery's 29 lines with 3 internal dependencies and 1 external.

* I wrongly counted spaces in jQuery's function while I didn't in Umbrella

Edit: the magic for the size of Umbrella JS is really through heavy code reuse and modern API usage. For this example, el.classList.add(name);