Ruin/Ruin II x3 means that you can cast either of those spells 3 times before the rotation of DOTs needs to be re-applied in a simple rotation. So my rotation includes 3 Ruin casts. I'm not including any CDs in this as they can be applied at any time and that affects DMG at that time globally which will affect your DPS, but that's not necessary to compare actions. Applying CDs will leave us with the same ratio of increase or decrease in DPS when comparing actions in most cases and it just makes it way more complicated.