My general take on the penetration system is that it's more a difficulty level issue than a problem with the system itself.
There was a brief window where it worked "well" -- after beta, before PotD was upscaled in difficulty, most fights had challenging Pen/AR but if you used buffs and debuffs appropriately you could get around the system and make it work for you.
PotD definitely needed the upscaling in difficulty but they changed lots of things at once, and one of the things they changed was increasing enemy AR dramatically across the board.
Net result, you now had to engineer every possible Penetration buff in a stack just to scratch anything, you'd often still underpenetrate or graze even after stacking every possible armor debuff, and the practical result was that the optimal approach was to bypass the AR/Pen system entirely via things like the combusting wounds / mind blades combo that just stack huge amounts of tiny damage dot's until it doesn't matter whether you're penetrating or not.
Problem is the fix for that would be to go through the whole game and renorm all the AR levels encounter by encounter back down again to sane levels -- basically, AR shouldn't scale with difficulty level the way other stats do.
All the other buffs and debuffs are a lot more granular but there's only so many points the AR scale can move on and the current PotD values are an overcorrection to the point of annoyance. I mean, I literally plan out my parties beforehand with a spreadsheet to make sure I get every available bonus and damage type and so forth and I still routinely run into PotD enemies where I'm better off just CW+MB than I am even attempting to bother to reduce their AR to manageable levels.
Edited by Dr. Hieronymous Alloy, 30 January 2019 - 08:05 AM.