Anytime you're asking this, go for the projects Quick Start / Getting Started doc. In this case here. If you're on a Debian based system Prometheus is already packaged in the repository so you don't have to download the latest. You likely won't win anything but the pain for having to set up the bare binary as a service with systemd. I followed that doc to setup mine but installed it from apt.
On a second thought, if you're getting it from the repo and it already has a systemd unit defined, it might be more difficult to follow the Getting Started doc. You know what, follow it as-is. Once you have something running and monitoring ad-hoc, it'll be easy to install from apt and put your config in it.
Applause for the analysis! ๐
I'm using a Pixel 8 Pro and my observations are similar. I let AccuBattery gather the stats you gathered and my numbers look similar. I'm also a Shelter user. I decrease my refresh rate to 60Hz and resolution to 1080p. The battery life is truly the best of any Android I've had so far.