Where do they imply the Pareto principle is the only type of distribution?

The author's claim is that postgres handles 80% of the use cases with 20% of the effort. It does not follow, as you recognize, that therefor EVERYTHING handles 80% of the uses cases with 20% of the effort. Where does the author imply that it does? Based on his characterization of Kafka I think he's say it solves a minority of use cases with a lot more effort.

I mean isnt this the explicitly made point by the author? That Kafka's use-case/effort distribution is different (worse)?