I still don't know what a "power user" is supposed to be, after seeing the term for like 30 years. Seems to describe a range from "able to leap tall spreadsheets in a single bound" to "the person in the office who knows how to fix things".
In my experience, most long-term unix nerds today seem to end up using (a) whatever is in front of them or (b) vanilla Debian.
I think a poweruser is a highly proficient and knowledgeable user. That means a Linux poweruser is comfortable configuring their system, writing shell scripts, installing software, fixing issues they encounter, etc. A Linux poweruser understands the layout and organisation of the system, so they tend not to lead themselves down blind alleys as much as beginners do.
I wouldn't consider myself a systemd poweruser, for example. I still haven't really wrapped my head around its operating model. I have to read the documentation too much, and I often think one thing is wrong but something else entirely is going on.
In my experience, most long-term unix nerds today seem to end up using (a) whatever is in front of them or (b) vanilla Debian.