I'd argue that horizontally sharded databases can work well, but they do tend to have significant non obvious tradeoffs that can be pretty painful.

There's a handful of companies that have scaled Citus past 1PB for production usage, but the examples I'm aware of all had more engineering to avoid capability or architecture limitations than one might like. I'd love to see someone come back with a fresh approach that covered more use cases effectively.

Disclaimer: former Citus employee