But is adding a lot of useful elements such a bad thing? The browser, being a way more efficiently coded application, would probably be a lot faster at handling the tag as well as displaying it along with the behavior and styles than a JS library.

Plus it can be easily designed by the browser’s developer to fit a native look and feel. Also, if the tag is never used, little to no time is wasted on dealing with the tag especially comparable to handling it all in JS.