There are points of disagreement between me and the author, although I wouldn't get too passionate about them.
Super-short version, reading over it again, is that XML is very good at what it does, but it really ought to be seen as a relatively specialized data format. It's really good at certain tasks, best-of-breed for a couple of them, and degrades rapidly as you get away from that. JSON is a fairly cheap & fast general-purpose format that's OK at a lot of things, isn't necessarily great at much, but as you get into more specialized use cases, also tends to degrade. Being a general-purpose format, perhaps arguably it degrades more "slowly", but it does degrade.
Properly understood, IMHO, their use cases don't overlap much if at all, and the combination of them may cover a lot of space, but are still far, far from the only serialization formats you'll ever need.
There are points of disagreement between me and the author, although I wouldn't get too passionate about them.
Super-short version, reading over it again, is that XML is very good at what it does, but it really ought to be seen as a relatively specialized data format. It's really good at certain tasks, best-of-breed for a couple of them, and degrades rapidly as you get away from that. JSON is a fairly cheap & fast general-purpose format that's OK at a lot of things, isn't necessarily great at much, but as you get into more specialized use cases, also tends to degrade. Being a general-purpose format, perhaps arguably it degrades more "slowly", but it does degrade.
Properly understood, IMHO, their use cases don't overlap much if at all, and the combination of them may cover a lot of space, but are still far, far from the only serialization formats you'll ever need.