As a DRK (and DPS scum observing DRKs), the key to surviving as DRK is burning CDs. A DRK that isn't at least lighting off dark dance every pull is going to make his healer very sad, and I can only vouch for myself as a DRK that uses dark mind on heavy magic pulls (ice sprite ambushes in stone vigil normal).

tl;dr: DRKs are mainly played by bads, and it's very likely that your healing isn't the problem.