alt Hacker NewsJSON Schema is largely an answer to people seeking that type of built-in validation. As I'm not a huge proponent for either (a tool is a tool and you work with it in its ecosystem), I don't have personal feelings on it's adequacy.
But, I would suspect, proponents of XML would still point to it's deeper typing system, document structure (especially the hierarchical features of it), and extremely mature ecosystem + tooling (such as XSLTs) as reasons to prefer it over JSON w/ JSON Schema.
Gotcha! Thanks for the rundown. I started programming at the time when we were transitioning from XMLHTTPRequest to Fetch with json so I know of XML but basically only learned about json.