I think you have make a distinction between "bad ideas of XML" and "essential ideas of CS that were implemented in XML because it was the fad at the time, and SGML before that, and are now being reimplemented in JSON, and will be reimplementing in the next big thing".

It's like complaining about regular expressions "Are we _really_ going to reinvent all the spectacularly bad ideas of Perl, except this time in Python?