Poisoner's Robes aren't much use to your average Barbarian! ("When the wearer casts a spell that deals Poison damage...")
I dunno ...
Sure there can be better bonuses, but on the other hand IF Larian extend its use so it will work for any posion damage ...
Imagine you will play your barbarian as Dual Wielder ... poison your weapons ... and just bcs you have this robe, that poison damage is effectively doubled ... that isnt exactly "bad" either. Especialy in case this is your only possible bonus.

Anyway i hope we shall move the right way and Ragzlin will drop his "armor" for Barbarians. :3
At least that design seems perfect.