Web Components is just a technology that is going through the teething stages, already Angular, React and Polymer is using it (React via certain webcomponents packages ). In Angular2's Web Components and the little bit I've done with Polymer, I've had similar experiences, it's fast, I don't see any advantage copying and pasting HTML anymore with Web Components giving decent performance in most browsers.
I believe it's a matter of time before all browsers will fully support the Web Components Spec, until then the polyfills that Polymer provides is pretty decent.
See here for the current adoption rate.