[DrFalkyn]

CAP has to do with distributed systems, not necessarily databases (unless they are also distributed)

Document databases/KV stores had a reputation for scalability/speed primarily because of the way they were used (key querying), and also popular ones such as MongoDB can do automatic horizontal sharding, not available in most freely available RDBMS. However you an also treat RDBMS as KV stores these days (with JSONB and simple primary key/index) if you want, and there are distributed RDBMS such as Cockroach and Yugabyte