The only thing I really liked about XML was schemas (XSD I think?). The ability to design a schema that could be passed around to let people validate the data

The only thing I really liked about XML was schemas (XSD I think?). The ability to design a schema that could be passed around to let people validate the data and structure of an XML file before sending it was really slick. The schema designer tools were easy to use. I actually enjoyed using WSDL based web services specifically because of this. You could take the file, which was just a schema and generate all the code and data structures you needed to interface with the API from any language…and you got the ability to validate your data client side before even bothering to send it. It definitely had some pain points, but overall these were the good points that I remember. GraphQL is probably the closest next evolution.