1. Normal oracles are super easy and they take 2 hits to kill in hard mode which 2 people with raid guns can easily destroy. 2. They also get obliterated by praetorians and die pretty easily in general also if your team is spread out inside the portal your team sucks 3. You can take out supplicants easily with a sniper or anything really. I would rate it titans<--- warlocks<--- hunters. As a titan I rarely die from enemies and blessing of light can keep a team alive while weapons of light can help your team kick ass especially with atheon. With the helm of saint 14 enemies that walk in to your bubble are harmless for about 5 seconds and the orb drops when enemies shoot it helps out the whole team. Void damage grenades are awesome for minotar and praetorians. Warlocks aren't anything special but the self revive is extremely useful. Their solar grenade spam can take out a ton of enemies and block off spawns. Hunters have nothing going for them. The roles you said anyone can do really and they may be as weak as warlorks in terms of defense but warlocks can self-revive while hunters can't. They're awesome at running away but not very useful since everything in the hard raid has -blam!-ing pinpoint accuracy.