Years ago I had a Graphite installation where I configured retention policies, and the same for InfluxDB if my memory doesn't fail me.

The downsampling feature at first glance seems to serve a different use case than Prometheus was built for, which I think is observability and alerting for a relatively short time period. For systems that need to work with years of data it totally makes sense, but I don't think Prometheus is used in those cases.

Since this feature has been built for a reason however, I could be wrong