I would think what happened was a bit of an exception - with 4x shaman at 78 the only DK's that are able to wipe my whole group are 79 and have 20k hp and are usually Frost. Granted a lot of good ones 76+ can take 1 or 2 of my shaman but the only thing that has wiped my whole group really is a arms warrior or frost mage casting blizzard from 40 yards away.

DId he just not even bother to cast or turn his alts? I just don't get it. When anti magic shield is up you just spam chain heal, or have all slaves bomb heals on the main and you can easily survive 12 seconds then the DK blows up. I just can't see a lvl 71 DK killing 5 80 shaman unless they were all afk.