I'm curious whether the parent poster knows about the most recent HA features in Postgres, such as those introduced in v10, and if so, what is still missing for comparable HA. Here's a link to the HA docs for out-of-the-box postgres:
https://www.postgresql.org/docs/10/static/high-availability....
As for scaling, it certainly scales out of the box with partitioning, but admittedly a partitioned table doesn't offer all the features that a non-partitioned sql table offers. A great assessment of the current state of postgres scaling can be found here:
https://blog.timescale.com/scaling-partitioning-data-postgre...