Spamming Ruin 2 is extremely MP inefficient. Even for Scholar and their Aetherflow. It has exactly the same potency as Ruin with almost twice the MP cost, and Blind has diminishing returns. Also, although SCH should be DPSing when possible, do not even bother if your tank takes so much damage Eos can't keep up. Granted this is rare in late game dungeons, it happens. The blind effect also seems to work on magic, so, if the Paladin isn't blinding, there's no real reason not to use it, but it's of a lower priority than healing and then spreading the DoTs.