It is easy to represent a graph in Postgres using edge and node tables. For the use case we have, it is more performant to query such a setup for many millions

It is easy to represent a graph in Postgres using edge and node tables. For the use case we have, it is more performant to query such a setup for many millions of relationships vs using the big names in graph databases. You just need a little bit of appropriate index selection and ability to read the output of EXPLAIN ANALYZE to do so. There are probably use cases where this doesn't hold, but I found in general that it is beneficial to stick to Postgres for this, especially if you want some ability to query using relations.