Except, I'd argue that most large distributed systems these days are using much more than two types of data stores, especially when you start including name/val

Except, I'd argue that most large distributed systems these days are using much more than two types of data stores, especially when you start including name/value keystores (and in memory caching variants), big data pipelines, transactional data, "unstructured" data storage (like Mongo), time series, etc. I work in FinTech and you'll see several backing our apps, and this isn't uncommon.