If the sk is casting plenty, I suspect you create a lot more white aggro than him. In that case he wants to use taunt to go to the top and follow it up with a dc and maybe second aggro spell to lock in his lead for a while. Make sure he is keeping haste up and has trained double attack.

I think the real issue might be someone is ccing the tanked mob with root and/or a spell with memblur component. Enchanters sometimes do this if they plan to cast a lot of debuffs on a mob, it stops the mob running at them.

I think your problems can be solved by using your own root.

Just get a Woodsman's staff until epic?