Since I haven't earned a single class set bonus yet (6 Torment-only set items so far, all from different sets), for me it's far from being mandatory (although it helps to milk the precious 3pc bonuses from crafted sets).
I think once you have perfect gear, i.e., found a lot of set items, the ring is mandatory, yes. SoJ+RoRG is probably the endgame ring for every class/spec. Unity is more for survivability and bypassing toughness requirements to get to T6, and it only helps in a full group; with 2 people Unity is not that helpful.
Since I haven't earned a single class set bonus yet (6 Torment-only set items so far, all from different sets), for me it's far from being mandatory (although it helps to milk the precious 3pc bonuses from crafted sets).
I think once you have perfect gear, i.e., found a lot of set items, the ring is mandatory, yes. SoJ+RoRG is probably the endgame ring for every class/spec. Unity is more for survivability and bypassing toughness requirements to get to T6, and it only helps in a full group; with 2 people Unity is not that helpful.