Here the author. I understand your points, I wrote a bit about my personal motivation behind this project.
http://rachbelaid.com/introducing-pome/
I also wrote within the readme about why wrote the project (context+goals), https://github.com/rach/pome#why-building-pome
This project is not aimed to replace more advanced tool like collectd but to offer a basic all-in-one solution. I'm also not planning to support huge database for the scaling problem that you highlight.
Trying to offer something easy without RDD store constraint for people who right now doesn't monitor their db.
I hope this make the goals behind the project more clear.
