And that is how you end up with massive data leaks.
Any API server can leak data. Most API servers define their own, native, completely one-off security system that does all checks in-app and logs into the database as a superuser. The framework-du-jour is basically an insecure rooted processes by definition.
PostgREST logs in with zero privileges. It then uses Postgres' native role based row-level security system to control access. Are you saying that is insecure?
What RDBMS did you use in on those times? PostgreSQL is pretty powerful these days(RLS, Extensions, FDWs, json functions, etc). I'm lead to believe that older RDBMS's didn't offer all the rich functionality we have today.