It is a master of plain old rbdms, but able to accomplish more with specific extensions. Sure, it probably makes more sense to use Elastic than Postgres for full-text search, but there is a solid extension for it. In a lot of operational contexts it’s easier to host another Postgres instance with a specialized extension than to try deploy an entirely new DB.
I agree with you, when you say its a master of RDBMS. But each extension brings its own baggage.
Specialised databases are written for a reason.
For majority of the people the extensions may fit .
But its not the best way once you want to optimise.
