as @JanVladimirMostert says, XML is more descriptive. If you need annotated data, XML is more practical (ex: list of movies with cast). Similarly, if you need highly nomenclature-d data, XML is better (e.g, defining node types and what they can or can't have as properties is easier in a DTD). If size is an issue, or if you want higher compatibility (XML parsers can differ, JSON parsers not so much), go for JSON.
So in summary I'd agree with the senior architects of your company that it is "better as a data interchange format", in the strict sense that XML conveys more meaning than JSON (after all the whole purpose of the -ML family was to semantically annotate data). As for which is better in a vacuum, it's a bit of a meaningless point. You could also go with URL-encoded strings, or your own custom format. If, say, the data you need to send is "user logged in" or "user logged out", you could go with an 8-bit identifier with a 1 bit flag. It all depends on the purpose of whatever data you're exchanging.
I'd say in the end it's about convenience. I haven't used XML in years because I have no particular use for it, and since I'm basked in JS most of my day,. Json is one JSON.parse() away. If I was using a framework with XML baked-in or part of the stdlib, I'd use XML instead.