A bit disappointing that (IIUC) for the common parsers you have to say everything twice, in HTML and in the accompanying JSON-LD form even though RDFa exists for the exact purpose of letting you point at the values already present in your markup. (Admittedly RDFa is perhaps too flexible for its own good when you just want to mark up some stuff, but if you’re writing a full parser anyway dealing with a bit of excessiv…
And then there is https://schema.org/ It's the item* attributes, e.g.: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/... Also Dublin Core in tags. Why do they keep adding conflicting meta data formats to HTML!?!
I think you should just think about what metadata you actually care about, and the main metadata I care about (choose your own list) is authorship, publish date, last update, subject keywords, thumbnail (OpenGraph 1200x630), and summary.
There’s a long list of additional metadata that I could put in my webpages because there are standardized ways to do it, but, why bother?