Parser correctness is irrelevant when you're talking about the ability to be written with few syntax errors. For instance, JSON has one type of string with one set of string escape rules. XML has element names, attribute names, attribute values, text nodes, CDATA content, RCDATA content, and more. And almost all of them have different rules for what they can contain and how they can be used.

By comparison, XML is orders of magnitude more complex than JSON.