PnS
What makes PnS so good?Unconditional Supplemental DMG
Its first skill, Purgatory’s Pact gives 50k unconditional Supplemental Damage to dark allies. Meaning every instance of damage (Ougi, Auto, Skill, Echoes) would have a flat 50k increase in damage with no condition needed, you just have to slot it in your grid.
It caps out at 100k, meaning you only ever need 2 copies.
Voltage
The second skill, Voltage II, gives 8% EX mod per Axe in the grid including itself,
the modifier is also additive so 2 PnS would give 16% EX mod per Axe and a total of 32% total EX mod from both copies alone.
Since Seraphic (Scythe of Darkherald) is an auto-slot for on element fights that would make it 48% EX mod which is big enough to remove the Astral (37% EX mod) for slot efficiency assuming you don’t need the auto cap up.
You do not have to always slot all the Axes into the grid. Usually you will fulfill the voltage naturally or close to the cap as you start to build your own grids.
Cap Up
The third skill which is only unlocked at FLB is Purgatory’s Quintessence, giving a total of 7% increase in damage cap at SL15. This is the ONLY reason why you’re uncapping the weapon, to make use of the cap up.
If you cannot make use of the cap, you can just use it as it is at 0* and it would still be a great slot in the grid, particularly for setups that have multiple instances of damage (Skills, Echoes).
Should you bar it or not?
For General Content, more Cap Up will usually translate to more DMG, and more DMG means higher honors
In Hard Content, having 14% Cap Up can make you clear certain parts of the raid easier, such as a 20m DMG omen, etc. There is still an issue of are you capping or not? If you cannot reach the cap, then any form of additional cap up is useless.