To be an effective tank, you also need to know what other classes are capable of bringing to the table. I'm not too sure how hard it would have been for the priest to Shackle some mobs, if any. (better for a spriest to do since they don't have to focus on healing) I can't recall what all can be shackled, but its just a suggestion. But, knowing what classes can do what can often be a saving grace, that or you just reform another group with a better composition..
Coulda had the lock kite one behind the group and then just fear bomb it...the lock should be able to solo that one, dots, sb, fear...fear...fear...if its still up..then its all urs!