I think the parent's complaint is a function of how your engineering org "uses" prometheus.

If you use it as a store for all time series data generated by your business, and you want to have indefinite or very-long-term storage, managing prometheus does become a challenge. (hence m3, chronosphere, endless other companies and tech built to scale the backend of prometheus).

IMO, this is a misuse of the technology, but a lot of unicorn startups have invested a lot of engineering resources into using it this way. And a lot of new companies are using it this way; hence the "one engineer's FT job".

I'd agree; I'm at a large corp that has a need to store our data for a very long term. If we were using Prometheus as an ephemeral/short term TSDB to drive alerting only, it would be really easy.

For reference: A single machine can push 5k metrics so you're saying a single prometheus instance can easily serve 20s of hosts. lol