IMHO, if poison deck can kill you, it's definitely not because Arsenic needs a nerf. Poison is best against those "dry" decks without healing, like Death itself - and Death is strongest here. I played Poison Dials for a long time, and I can tell you that sometimes 2 Sanctuaries, or 1 Empathic bond is more than enough to own every Arsenic of this world, nerfed or not.