I certainly agree with you. As engineers, we should be comfortable with properties and requirements, and selecting the combinations of tools and self-written code which match them most maintainably.

Unfortunately, it's easier to think in terms of tools and substitutes. For instance, it's difficult for us to say "I used a combination of handwritten code and redis to provide some of the guarantees that I would've got for less handwritten code and Postgres". However, this is exactly that sort of article: it argues that sometimes, it is better to use Postgres even if the features you want a more naturally provided by Redis.

> And there I'm unsure what we consider essential characteristics of a database.

I doubt there really is anything. I don't think it's possible to actually narrow down "database" to some precise definition, so I think for instance the person who said "only an idiot thinks Redis is a database" needs to explain what they mean by "a database" before we can discuss the merits of their position.