Earlier quoted context omitted.
You can get really far with database views (decorating data, especially), functions (all sorts of biz logic) and Postgres roles for RBAC. But I hear you on integrating with 3rd party APIs, etc. Fwiw, there's a number of PostgREST backend client libraries to help with that.
I presume you mean postgres client libraries? Or have I missed a postgrest feature?
https://postgrest.org/en/stable/ecosystem.html#client-side-l...