My 41 conj found these quite fun and challenging but easily beaten unless something went wrong.
I even defeated the arena champion after a few tries.
What i use on those group gnolls:
Target a caster, start casting shattered earth.
Before shattered earth finishes casting i send the pet to attack (if you use pet too early you can get stifled)
Change targets and cast hunters, rockslide and tremor.
Change targets and burn down remainging mobs.
Works well for me, after lv 35 petrify will not work and our other stuns are a joke with 3sec cast time and high resists.