Dear Ihe,
I partly agree, partly disagree. Here are a few thoughts.
1. I would not discard JSON as a viable syntax for arborescent data, and neither would I discard XML. Each of them has its sweet spots. XML definitely surpasses JSON at document-oriented data. More precisely, I mean here with "documented-oriented" mixed content encoutered for example in the publishing industry (this is different from “document” as in "JSON document" or "XML document”), such as
<p>This <i>is</i> <b>a sentence</b>.</p>
which cannot be achieved with JSON in a natural way. And of course, JSON has its nice sweet spots, too, in particular in the absence of mixed content and when there are more regular patterns in the data.
2. The fact that JSON is smaller/simpler/more lightweight than XML can be advocated reasonably and with objective criteria by, for example, comparing the size of their respective specifications (I mean here the syntax only, not the schema/data model/querying ecosystem around them). An introduction to the JSON syntax (it fits on json.org’s homepage) is definitely shorter than one on the XML core syntax. This is neither good nor bad, as each syntax has their usecases.
3. XQuery was extended in its latest version with maps and arrays (and, as it was a low hanging fruit, support for JSON input/output). This demonstrates that JSON is relevant in the tree-like data landscape, at least as a good complement to XML.
4. Granted, the same “errors of judgement” are regularly repeated when new syntax gets invented: first, one thinks that one does not need all the complexity of existing syntaxes. And then, with time, one realizes that one needs this data model, and that schema language, and that other query language, and an update language, and so on. Still, this realization is a good thing.