Thanks very much guys, that makes more sense now. I kinda figured Ruin II was better as a one-off thing for the blind effect (well, at least in the field), but just wanted to confirm with someone else.

I do have more questions regarding Fester though. It's an Aetherflow ability. So at the moment I have three: Energy Drain, Bane, and Fester. Since I only have two stacks of Aetherflow at the moment, how do I go about making the most out of them?

I apologize if I should have figured this out by now, but I will say I haven't had any complaints as ACN/SMN in dungeons and trials so far, and I really would like to keep up the best effort I can in playing my role, at least up until endgame where things get... really ugly, from what I understand.