This is a very narrow definition of a time series DB, really more of a pure metrics store that requires individual time series to be kept separately. I find it odd, as I wouldn't define time series DB, in general, to be what they are. Rather, a time series DB is usually simple some sort of DB that supports a time column as the main index. There's tons that fall in that category (including Postgres, which you should absolutely use unless you have a compelling reason not to) that can easily handle many of the situations the article claims won't work. Druid can handle high-cardinality, for instance.