Well you obviously don't issue metrics queries over arbitrarily large datasets, right? The Prometheus architecture reflects this invariant. You constrain queries against both time and domain boundaries.
It scales so well that many aggregations are set up and computed for every service across the whole company (CPU, memory usage, error rates, etc.). For basic monitoring you can run a new service in production and go and look at a basic dashboard for it without doing anything else to set up monitoring.
Requiring query authors to understand the arrangement of their aggregation layer seems like a reasonable idea but is in fact quite ridiculous.