More to database architecture than performance? Won't someone think of the data modellers?
The motion is about providing a 'significant advantage' but only raw read/write query performance advantages seem to be used in support. For use cases with a lot of many-to-many relationships and objects that can be linked to the same other objects for different reasons at the same, the significant advantage isn't performance but ability to model with reasonable clarity, and I'm sometimes very happy to sacrifice performance for that (especially when performance is still perfectly reasonable). The way real world things relate to other real world things is rarely a neat, hierarchical relational model with nice foreign keys, and sometimes modelling as a graph has a 'significant advantage'. (And before someone mentions it, if your RDBMS model is full of FK to FK mapping tables with added relationship meta-data, then you've just built a graph, and your SQL will be 'interesting' and hard to manage)