It is not good for human persons or the existing web of documents. It's only good for the megacorps' intended not-web of applications. So this is how the web dies...with thunderous applause.
Every major browser supports web components at this point. Purportedly it’s a ‘Google’ standard & Mozilla & Microsoft are only supporting it because it serves them as mega corps?
Why do you consider it ‘not good for humans or the existing web’?
Anyone and everyone who wants to can write web components, and they will work in all major browsers. No dependencies, No libraries, no 3rd party APIs. Just vanilla HTML, JS & CSS.
To me that seems like a great advance for regular humans. We can develop ‘complex’ JS components with existing web tech. No build step, no learning 3rd party libraries.
One example of where this goes wrong is if, say, you wanted to implement the indieweb protocols for p2p social networking. With webmentions it's a bit like pingback, but instead of just HTTP POST, the pinger has to have a link on his webpage linking to the pingee's URL. That means the pingee webmention implementation has to be able to parse a page and get the html. With webcomponents doing DOM stuff instead of having HTML text that webmentions implemention (and everything else) has to become really complex instead of a simple curl and parsing text.
(1) recent whatwg html standards say this is all fine and dandy because whatwg is run by corporations for corporate needs. But it isn't fine and the needs of applications are not the needs of documents.
I often use the term W3c Web Components to differentiate from JavaScript components that use other APIs.
I know that Web Components are a recurring topic in W3C meeting agendas. I am not aware about parallel fast track discussions in WHATWG, but that makes sense.
I think there are already two Webs (simple and complex) and Web Components are actually a good way to create progressively enhanced websites that work well in both.