I have a cleric aswell but hes Pyro/Hydro with man at arms. I focus mainly on hydro and man at arms. My cleric and jahan are my main healers and buffers. I think your problem is your not using fire against the undead, my cleric has pyro skills like flare, Burning Up and small fireball. Flare actually came from ring i picked up. I also use Wildfire which is a Haste buff. Jahan should be your main Air/Hydro user. I think you should either reroll or focus on Freezing/slow the biggest threat and ganking the others. Hope you got something out of that.