I'm really surprised the Warlord is so far ahead. Healing is what the leader is all about and Clerics dominate, especially with the addition of Divine power.
It your foes are played intelligently, they will easily focus fire down group members and the poor healing of the Warlord will not pull you through. Granted some fights the enemies shouldn't fight as effectively as others ( lets say oozes as compared to actually intelligent foes ) but in general if your foes are intelligent they will use the same tactics as PCs, the most important of those being focus firing.