I've recently hit a very similar problem. There's various problems with the web components (like he mentions) and I wanted a better way to write plain html with components. I ended up making a tiny python build script to process fake html components into proper HTML: https://github.com/shminge/builder

I've designed it for myself, deliberately to work around the flaws with web components mentioned. It hugely speeds up my process of writing pages for my blog (after trying everything, I've ended up just writing plain html) because I can define a component that holds all the boilerplate of the page (header, css, etc) and then write my pages as `<pagelayout> <p> body content here </p> </pagelayout>` and have that be expanded into proper valid HTML