Earlier quoted context omitted.
In what way is JSON a step down versus XML? Frankly I get nervous and sweaty every time I need to deal with XML, because of the inherent performance/security issues it brings into my codebase.
XML is much more precise and much more flexible. It also benefits from much more powerful and mature tooling. The few comparative downsides it has include verboseness, which doesn't matter to machines, and that younger devs don't know how to work with it, which again shouldn't be much of an issue in this use case.
JSON is over two decades old. XML is only five years older. Both have powerful and mature tooling; I'm not sure how you can suggest otherwise.