Originally Posted by
Dugarax
WARNING: This is a post exclusively concerning Armor Penetration Rating in PvE
Warriors used to stack ArP (Armor Penetration) before the patch until the cap, which was 1050 with Madness of the Betrayer and 1350 without it (assuming the said warrior had executioner on one of his weapons). The principal interest of ArP was that it scaled with itself making it a better stat when you had more. 7 ArP was considered equivalent to 1 str for warriors with low ArP, and was worth more as you gained more ArP.
Now everything is converted to a rating, meaning it will ignore the target's armor by a % AFTER the debuffs and buffs (sunder armor, expose armor, faerie fire, executioner, etc.). Assuming the numbers in this thread are correct, the value of ArP would be as follows:
1% * 1350 (Boss' armor after debuffs) = 13.5 ArP
13.5 ArP = 15.83 ArPR (Armor Penetration Rating)
13.5 / 15.83 = 0.85
Each point of ArPR is equivalent to 0.85 ArP. The itemization cost spent on ArPR is almost the same as Str, so on 2 items with the same budget spent on Str and ArPR, 1 Str point = 1 ArPR point.
Since 7ArP was generally considered equivalent to 1 Str before the patch and now that 1ArPR is worth 0.85 ArP on a fully debuffed boss, we can conclude that ArPR is a significantly inferior stat compared to other stats like Str, Crit and Haste. Its value however increases with a target's armor, and level 80 bosses are expected to have much more armor than level 70 bosses, so this might change.
To make ArPR marginally equivalent to Str (make 1 ArPR = ~7 ArP), the target needs at least 11,000 armor, 11,081 be exact, to have 1 ArPR be worth exactly 7 ArP (see calculations below).
1% * 11000 = 110
110 / 15.83 = 6.95
I understand these maths are more accurate for warriors, but the value of ArPR can't be much different for pallies, and it can only go down compared to warriors since warriors' damage is 100% physical and not paladins' damage.
I may have made minor or major mistakes, but this is what logic and maths lead me to right now.
TLDR; Armor Penetration Rating is currently an significantly inferior stat compared to Str, Crit and Haste in PvE, on a fully debuffed boss.
Edited a few times for clarity/confusing sentences.