XML can be a bear, but sometimes you need a bear.
"XML is like violence. If it doesn't work, you're not using enough of it."That same saying would also work replacing XML for soap (but not SOAP).
I do agree with the XML criticisms around writability and complexity, though I think if you made a Venn diagram of the actual complexities inherent in managing a multi-client document-exchange system and the complexities of XML+Schema, you'd find that they're similar--and that many people who start building such an exchange with JSON documents end up stumbling into the same amount of complexity except in an ad hoc fashion.
It's funny, I wonder if other people have the same surreal experience: as the mass zeitgeist moved away from XML I was more or less like, okay, gotta go with it, as the driftwood goes with the currents. It's interesting how the zeitgeist functions. You can tell it's happening when people look at your functional system and are like, "Uhh, why aren't you using X...?" as though it's self-evident that you should drop everything and rewrite. Where X was, over the years (dating myself) {"Java", "PHP", "Node", "Rails", "Jquery", "REST", "Angular", "React", "Thrift", "NoSQL", "Protobuf", "Hadoop"}. Some of which I quite happily used, BTW, so the interesting part is the penetrative nature of the conversation, e.g. how the quite-functional-but-not-hot technology becomes the sick gazelle falling behind the herd, even as it is not empirically sick.
And then the ratchet turns, and the pendelum swings in reverse, and suddenly that thing sent from god was instead discovered to be sent from satan... and you're still trying to explain that tradeoffs exist
This coming from someone who hates XML, avoids it at nearly all costs - there are times it's the right tool for the job. And you list that time. If you have a 1-1 API contract, don't use XML. If you have 1-N, don't use XML. But if you have N-N API contracts? Where you're talking to half a dozen other services, and they're all talking to you? XML is an excellent choice.
Fine, but with for example, Protobuf, you share a .proto file and so there's zero percentage chance of this happening.
Good times.
But let me tell you how much I appreciated XML and schema validation when we were working with fifteen different partners all using a standardized XML format with a schema. These are cats who were putting XSDs into their IDEs, clicking generate to get a class, and then just not caring.
So when our integrations broke because they were sending XML payloads that failed schema validation, our conversations were so easy.
Before you say "yes but technically you could have done the same with $OTHER_THING" -- sure it's possible, but XML is ubiquitous. Shit, our tools were in Ruby.
XML can be a bear, but sometimes you need a bear.