Postgres violated serializability on a single node for a considerable amount of time [1] and used fsync incorrectly for 20 years [2]. I personally witnessed lost data on Postgres because of the fsync issue.

Database engineering is very hard. MongoDB has had both poor defaults as well as bugs in the past. It will certainly have durability bugs in the future, just like Postgres and all other serious databases. I'm not sure that Postgres' durability stacks up especially well with modern MongoDB.

[1] https://jepsen.io/analyses/postgresql-12.3

[2] https://archive.fosdem.org/2019/schedule/event/postgresql_fs...