My problem with an understanding of progressive enhancement as ”simply sprinkle vanilla JS on top of server-rendered HTML” is that it falls behind all robustness practices and abstractions developed in the last decade.
I had a similar impression when reading this article: https://www.jayfreestone.com/writing/web-component-libraries/
The conclusion disappointed me. Web Components either require manual wiring and low-level DOM code. Or they render full templates like Lit. This duplicates server templates unless you SSR.