I’ll say XML was flawed. It was a great initiative behind the wrong data model. The idea was to take what made sense for documents (strings with markup) and use that to represent everything else. But most data structures are really awkward expressed that way, and you run into weird decisions like: Should my map be a list of items or a set of attribute pairs in a single node? Is the key a node or an attribute? When does order matter? Etc.

If the XML standards group started with JSON or YAML or .. anything else, I think they would have made something really useful. But we didn’t think of that at the time, so instead we have XML. An impressive monolith built on a dead mountain.