Very nice write up! It makes even more sense if you compare with Azure and see that they have the same kind of offering with the exact same breakdown, i.e. Azure Database for PostgreSQL/MySQL which is the managed relational database solution, Azure SQL databases which is the in-house one (i.e. SQL Server modified for Cloud) and promise cheaper/faster/higher HA because that's their own opinionated technology, with serverless and hyperscale (i.e. limitless) configuration options. They don't have DSQL equivalent yet, but their NoSQL offer (Cosmos DB) already have SQL query language support and with some modifications & improvements could be their "best of all worlds" equivalent.
