However, you didn't return to postgres:6.0 (first formal release in 1997 [1]), you returned to postgres:latest, which included the lessons learned from lots of other databases, thinking here of postgres:9.2 (in 2012) adding native JSON support making Postgres basically NoSQL with extra steps. Contrary to popular wit, reinventing the wheel is always beneficial, if it will not bring something new to the world, it will at least make you understand and appreciate wheels better.

[1] https://en.wikipedia.org/wiki/PostgreSQL#Release_history