I'll start this off with two points!
Ruin: Here's the question: Why would you EVER use ruin? Lol.. I mean.. why is it even a cross-class? Unaspected damage appears to be worthless. Elemental properties are ambiguous at best right now, and Yoshi's worries about elemental rock-paper-scissors excluding some classes (especially casters -- what happens to THM if mob is resistant to fire and/or ice?) seem to be preventing any further impetus in that direction. Even if elements mattered, Scathe does the same thing for 140 pot as an instant cast. So..what? Is there some perk I'm missing? Does it ignore defense or something?
Virus & Eye for an Eye: I WANTS IT. I could see both of these being skills all casters need to have (I believe WHM can equip as well) for end-game raids. I could see virus being especially OP if it stacks on the base str/dex value. Any 24-man raid with 10 mages could turn a 100% str/dex reduction for 10 seconds every 120 seconds. If they all had eye for an eye (and it stacked similarly on base), they could effectively make the main tank invulnerable for 10 seconds out of every 60 if properly coordinated.