Played both SCH and SMN...I never use Ruin I unless in a low-level dungeon that requires it. Everyone says that Ruin I is more MP-efficient, and that's true, but I have never been in a situation where I was so low on MP that I couldn't afford Ruin II. Ruin II can't be interrupted from moving to dodge mechanics, or from knockbacks. It's not that expensive. People used to say the same for SCH too, that don't spam Broil because it eats up your MP--but I can spam Broil for days while also throwing Succors and Adlos and never come close to running out of MP. This is even more true when overgeared for content because spell's MP cost is based on Level, not iLVL and most mage iLVL stuff has free Piety on it which means you have more MP for casts. Also, I may be wrong, but isn't the amount of MP you auto-regen based on your Max MP?