Most of our use-cases for the built-in json support in PostgreSQL is not to implement schemaless design storage, but instead to remold data.
One of the common cases we use json support is what we call UNPIVOTING data.
We demonstrated this in Postgres Vision 2018 presentation in slide 23.
This trick won't work in other relational databases that support JSON because
it also uses a long existing feature of PostgreSQL to be able to treat a row as a data field.
Unfortunately there are no slides of the pgRouting part, except the one that says PGRouting Live Demos because Leo will only do live demos. He has no fear of his demos not working.
Side note, if you are on windows and use the PostGIS bundle, all the extensions listed in the PostGIS box of the spatial extensions diagram, as well as the pointcloud, pgRouting, and ogr_fdw are included in the bundle.