> Often in the real world you need tree-like structures, which are fundamentally not able to be represented by a table/relation. No amount of joining can produce anything other than a table/relation. The n+1 problem is introduced when you try to build those types of structures from tables/relations.

You can easily get hierarchical output format from Postgres with its JSON or XML aggregate functions.

You can have almost all benefits of an embedded database by embedding your application in the database.

Just change perspective and stop treating Postgres (or any other advanced RDBMS) as a dumb data store — start using it as a computing platform instead.