Exactly. People overestimate the amount of effort and cleverness it takes to horizontally shard/scale your data yourself rather than trust a specialized databas

Exactly. People overestimate the amount of effort and cleverness it takes to horizontally shard/scale your data yourself rather than trust a specialized database to do it as a black box. And overestimate the cleverness of the black box. What you retain by staying with Postgres rather than going to a more exotic database is priceless. There is a threshold of data size or product need that makes a more specialized database the right choice. It's just well above 100 GB and your application should have some very specific needs to justify it.