Anyone who puts in minimal effort could check the combat log vs potency and do some math. Or compare threat vs the equally geared players of the same classes. Or read a guide.

Even without a dps meter you can optimize dps by pure theory craft and combat logs. (parsers make estimations half the time this is the better route anyway).

People unwilling to do this minimal effort, lazy/bads/very casual players, are who he is protecting. It makes sense, they are probably as much or more revenue for SE then anyone else, and it does make it harder to harass obviously bad players. It is not very effective in the end though. While it does mean pseudo elitists will have trouble calling people out it does not stop anyone with minimal knowledge of game mechanics from doing so.

As long as a combat log / threat meter exists. I will tell people when they are under performing and abandon any duties I find to be a waste of my own time. This is all without the mention of any parse or dps meter.