Theorycrafting is almost always done in PPS. That being said, If a level 70 normally geared paladin and a level 70 normally geared SAM both do 100 potency, do they do the same DPS? (note: if I have a 10% damage buff we could say 110 potency, so we arent going to consider that).

A tank has substancially lower main stat after the change and historically bards have had lower weapon damage, iirc paladins sword + shield is less stats than WAR's 2 handed axe.

While PPS is easier to work with, the end goal, and what we ultimately care about, is DPS. "Random" or "Luck" isnt a factor, if you have enough parses to average out the outliers.