Is XML better than JSON? For longterm stability sure. A quick config file? Nope. You see, to understand XML you kind of have to know how to work with trees. Bread-and-butter for compsci grads, a nuisance for all others.
Recently I needed to query a SOAP-based API. It took me 3 days because I had no idea how a namespace in XML worked, because I was not sure which lib in Python to use (lxml was the solution), and because their API had some quirks. I read forum posts from the late 00's, the documentation is really scarce.
I would love to learn the fundamentals, I don't like half-assing things. But a) I'm not going back to uni for it, b) I'm not bright enough to be excellent in two fields. Learning the fundamentals takes a very, very long time. Where to start even? A complete math program? Programming fundamentals as such? Theoretical compsci?
At the end of the day, things need to work. If they fall apart next year I can tell my boss "ooohhh big problem give money". Using XML instead of JSON has no payoff today.