I use LitElement pretty extensively, which is a wrapper around WCs, and I like it quite a bit - but it's only a minor improvement in my mind compared to React, and that improvement is just reducing the abstractions from the DOM API. It's still a mega codebase.
I've also tried multiple times to just work with vanilla WCs, and it's sensible only up to a very limited point. If you got a JSX/lit-html module involved it would go further, but at that point it's pretty past "vanilla." And even then, you're not in the realm of "just using HTML."
Author lays a lot of that on the developers having a proclivity for JS, and that may be true, but I've been trying to figure out if this is just complexity in the stack that hasn't yet be solved. UIs are complex, you have lots of stateful interactions between them, and I'm really not sure what the right solution would be for a "do lots via HTML" goal.