No. They’re saying that it’s creating an entirely separate DOM tree unnecessarily by using shadow DOM where it isn’t needed.

On a related note, I’m curious if anyone has a benchmark comparing performance and memory consumption when attaching a shadow root vs not.

It's more than one unnecessary level of nesting in the DOM, it's that they're creating an entirely separate DOM tree they aren't using. I threw together a test using tachometer to demonstrate the differences: https://github.com/jjcm/shadowTests

The results are here: https://raw.githubusercontent.com/jjcm/shadowTests/master/re...

TL;DR - the withShadow element takes about twice as long to render as the withoutShadow element. Don't use them unnecessarily.