I would not use it. Common mobs have no resistances, so the set will do nothing. Bosses vary. 18.2K is the top end, but not all bosses have that much and I suspect not all can be set off balance. If you're talking dungeons or trials, you now have tanks removing 9K armor from a boss with Pierce Armor. There are also other debuffs placed on the boss and your CP are also aiding penetration. Therefore it's a no. Don't use Stuhn for PvE.