XML per se is great for storing tree like structures. However, it's not actually XML that's bad, but content editable, which is what most editors were using until recently.

In content editable, the visual information is not one to one transferable to a single html document, which, in turn, means not transferable to a single XML representation (and in all likelihood, the html is what is used as the representation, not a transformed XML document).

With Json representation , the content editable method is no longer the path of least resistance. Building out a proper renderer (whether in canvas or dom) means you end up removing most of the content editable issues.