If you use Ruin as a SCH, I'm sorry, but you are absolutely terrible. There are so many advantages using Ruin II over Ruin as a SCH I don't even know where to start:
1 - Instant cast, no aoe will ever force you to interrupt this spell.
2 - Can autoattack once per Ruin II, meaning every Ruin II will have around a potency of ~100-105 instead of 80.
3 - Can do emergency healing in case someone takes damage without having to interrupt anything. You are just say casting your Ruins II against a boss, tank gets a big hit, ac lustrate <tt>. If you were casting Ruin, you'd have to interrupt the cast and cast lustrate, a lot more trouble.
4 - The 3 reasons I gave above should suffice. The mobility you gain from using Ruin II over Ruin should really just be enough, despite mobility not being the only significant advantage you obtain from using Ruin II over Ruin. What is more, if you are running out of mana with a 4500 SCH because you are using Ruin II, uninstall.