You are right, PostgreSQL is not necessarily optimal for time-series workloads. In this case, the benchmark is a simple task, and not related to time-series. It's consists of reading 1 billion values to a table and sum them together. It doesn't get simpler than that.

The reason we are showcasing this instead of other more complex queries is because this is a simple, easily reproducible benchmark. It provides point of reference for performance figures.