So you're calling Graphql via PostgREST, but I didn't ready about why you're including Graphql in the first place. Isn't it orthogonal to PostgREST which is already used in your stack?
PostgREST does solves a few of the core challenges that GraphQL is intended to address like over/under-selection and resource embedding (relationships).
Even so, there has still been a lot of interest in GraphQL so users can leverage the growing ecosystem for things reflecting the data model/types for client usage, offline caching, etc
