That said, over time PostgreSQL has wildly expanded the range for which it's suitable and if you can and want to bet on the future, it's often a better bet than niche systems.
It's also important to remember that PostgreSQL is decades ahead of other systems in data virtualization and providing backward-compatibility to applications after changes; pushing down computation near the data and avoiding moving billions of rows into middleware, including a world class query optimizer; concurrent data access; data safety and recovery; and data management and reorganization, including transactional DDL. Leaving this behind feels like returning to the stone age.
I'm not sure what you mean by ultra low latency but unfortunate to have to rethink what a tool is good for because of RDS / EBS.
There are even other AWS Postgres-oriented options (check the pricing first):
ZeroETL from Aurora Postgres to (postgres-compatible) Redshift (Serverless?)
But to pick the wrong DB tool in the first place and bemoan it as “not scalable” is a bit like complaining that S3 made for a poor CDN without looking at how you’re supposed to use it with Cloudfront.
(I would like to know, where their ZeroETL originated from, usually AWS picks up ideas somewhere and makes it work for their offerings to cash in. A universal replication tool.)
After that is when I'll start migrate to duckdb or clickhouse (or citus if I don't want to move out completely from Postgres)