There's a long standing standards issue for this: https://github.com/WICG/webcomponents/issues/909

While you can easily turn rendering to shadow DOM off on a per-component basis, that removes the ability to use slots. It only really works for leaf nodes.

Pulling a stylesheet into every component is actually not bad though. Adopted stylesheets allow you to share the same stylesheet instance across all shadow roots, so it's quite fast.