> First off, what’s with the pointless JavaScript? There’s no need for imperative code here.

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....