I'd argue that (JSON plus API description and generation tooling) didn't really deliver everything. XML has schemas and validation as part of the main standard

I'd argue that (JSON plus API description and generation tooling) didn't really deliver everything. XML has schemas and validation as part of the main standard. JSON still doesn't have that. There are some things tacked on that 90% of people don't use. XML has comments, JSON doesn't (!). JSON is okish and it's easy to pick up. As Visual Basic, Javascript, PHP, Ruby, Python, Golang have proved, convenience at the start beats almost everything else.