Exactly, I'm not sure why you've included the JS. The whole point of the Declarative Shadow DOM is to create shadow roots declaratively, rather than imperatively. To quote web.dev "This gives us the benefits of Shadow DOM's encapsulation and slot projection in static HTML. No JavaScript is needed to produce the entire tree, including the Shadow Root." [1]
[1] https://web.dev/articles/declarative-shadow-dom#how_to_build....
It's a pipe dream that doesn't work in practice. Because on its own declarative shadow dom is useless.
The example I was responding to was using the Declarative Shadow DOM. My comment was intended to point out the simple fact that the imperative component definition the author was complaining about is superfluous, meaning you can safely remove that entire script from the example.
DSD is useful for SSRing web components, which allows them to render and work without JS. But honestly, I don't get the obsession with doing stuff without JS, it's part of the html/css/js trifecta.