For all practical purposes Ruin III is now Ruin II which was our old Ruin spam. There is no reason to keep the MP costs as high as it is for the lower potency. Heck lower the MP and keep it the same through the Ruin IV proc if they need some balance. If they replace Ruin I into Ruin II at level 38 and lower its MP to let's say 360 then change Ruin III to 720 when not in DWT it would fit the current play style better.