To my mind, the point of databases is to provide as accurate a representation of some aspect of external reality as possible. The advantage of graph databases is that they model the world as things that have properties and relationships with other things.

This is closer to the way that humans perceive the world — mapping between whatever aspect of external reality you are interested in and the data model is an order of magnitude easier than with relational databases. Everything is pre-joined — you don’t have to disassemble objects into normalised tables and reassemble them with joins.

In this respect, even the simplest graph database such as Neo4j — which models the world as a bunch of JSON documents, some of which may contain pointers to other JSON documents, is much better than even the fanciest RDBMS. Granted there is no taxonomy or schema, and support for temporality is basic, but it’s easy to produce a much more naturalistic model of the world than will ever be possible if you have to break the things up into relations.