Thanks for your reply, BinaryIdiot.
The gold standard also ensures accessibility (the responsibility for accessibility is transferred from browser maker to developer). I suspect many developers, even Google in some of their examples, will forget to add it or think it doesn't apply to them/their app, I find this a huge concern (the web until now embraced accessibility as a universal value).
Web Components are not ‘just’ composites of plain old HTML, some styling and JavaScript, they require tooling and polyfilling (and some polyfilling will make apps slow for users that don't have the latest tech). This is potentially bad for new people in the industry (have to learn many tools before they can get started), and bad for users (as their device might be toos low).