For the benefit of the probably only two others in the studio audience (who are probably currently both facepalming), we tested with multiple libraries, multiple languages, multiple OS and multiple data subsets. We found in our particular experience that JSON worked the best across our criteria using a representative sample of our datasets. Nowhere did I say XML is always the wrong choice for others. I vaguely recall I wrote I'm now none too keen on XML but have used it in the past. For some things I'd actually choose TSV over XML but thats on fairly, hopefully, obvious cases. I think XML's verbosity is actually its strength but that it has tradeoffs which are quite real. This should not come as a revelation to anyone.
I shared a necessarily limited snapshot of an experience I had and an opinion I formed based on it. I think others can do their own testing as I expect they will anyway. They will confirm or deny based on what they are doing. Especially the opposite case of large imports in XML being faster than everything else. That's completely fine by me.
You've definitely made too many assumptions based on too little data. You didn't even ask what industry this was for. Or what kind of data it was. Or even what disparate systems were involved such that we'd end up with something you state are inappropriately large compressed text files. You disregarded the use of "keywords" such as gigabytes or even compression in general as if those should be unimportant to us. Or why we would use JSON at all. Then you make judgements. Fairly condescending ones at that. This shows a general lack of awareness across several aspects of life in general. For the sake of both of those other people still following this chain, I'll finish here. Life is too short.