> All in all, my impression of MongoDB now is that they're one of those "fake it till you make it" success stories, where they leveraged their popularity into enough momentum to fix most their major problems.
That's not all bad. The same could be said of MySQL. Both DBMS prioritized ease of use over data integrity in the early going.
And yet PostgreSQL making the exact opposite choice has really paid off in the longer run. People used to dismiss it as simply a toy for academics to play with, and look where the project is today. It can easily surpass most NoSQL databases on their home turf.
To be fair PostgreSQL 15 years ago also had a lot of problems storing data reliability. Some of them manifested as performance issues. I also heard a fair number of war stories about corruption with "large" databases (e.g., 1TB+). PG replication lagged MySQL for many years as well. These seem to be non-issues today.
At this point there's effectively no difference in the durability of data stored in MySQL or PostgreSQL, so it's hard to argue that one or the other made a better choice. They just got there by different paths.
In fact, PostgreSQL is winning back share in part because of licensing. GPLv2 is limiting for a lot of applications, and there continue to be concerns about Oracle ownership. It's also absorbed a lot of features from other databases like JSON support. That's not special to PostgreSQL though. It's been a trend since the beginning for SQL RDBMS and explains why they have stayed on top of the OLTP market for decades.
That's not all bad. The same could be said of MySQL. Both DBMS prioritized ease of use over data integrity in the early going.