Your last point is a very telling one. Healers are already forced to stand still in order to deliver their heals. So any attack that let's you stay on the move is very welcome. As Sch I'd always go with Ruin II over Ruin if it is an option for that very reason. I also have to say that a SCH could usefully run in, pop Miasma II on a pack, once the tank has aggro, and then retire to a safer range for healing. Instant cast attacks are awesome when you are otherwise rooted to the spot to cayrry out your role.