Comment by skywhopper

Ultimately, I think the problem is that everyone thinks we need to be able to do all the same things with structured, hierarchical data that we can do with normalized, relational data. And it's like going from 2-D to 3-D. Things don't get just twice as complicated, they get exponentially more complicated as the problem-space and schema complexity grows.

Thus any toolset that tries to address relationships, schemas, searching, and grouping in an XML/JSON type data format is going to be exponentially more complicated than RDBMSes and SQL.