You are right in saying that the docs lack "the big picture", but that will be fixed soon(ish).
The big picture is that it's not PostgREST alone that accomplishes this "big claim" of eliminating the need for custom APIs. It's the combination of using openresty(nginx)/postgrest/postgres/rabbitmq together that gives you the possibility of "defining" apis rather then "manually coding" apis.
Sounds like an interesting tightrope walk. I feel a bit of concern about the number of moving parts being part of a single solution, having configured similar selections of software myself, but I'll wait and see. Best of luck.
Fair point. I can't really judge until I see some kind of overview that deals with the pragmatic aspects of working with it, or trying it myself (which I may do some time).
The big picture is that it's not PostgREST alone that accomplishes this "big claim" of eliminating the need for custom APIs. It's the combination of using openresty(nginx)/postgrest/postgres/rabbitmq together that gives you the possibility of "defining" apis rather then "manually coding" apis.