lol 1 ruin II might not make a difference but think about in 5 minutes of a fight how many off GCD abilities you use.

raging strikes, rouse, spur, enkindle, aetherflow, bane, fester

If you use ruin II between them that's an extra 560 potency you won't have just from using those 7 skills one time. Ruin and Ruin II basically are like adding an 80 potency dot to your rotation and you should always use them in your GCD slots without wasting any time if you are not busy refreshing dots in my opinion.

Who cares about blind though honestly. The tank is not going to depend on blind for survival. If the tank needs blind to survive you won't win anyways.