4 warlocks don't have the same AOE potential as 4 Mages, but they are less glass cannon prone. I always played my mages fast and loose, always taking huge pulls, often losing 1-2 mages every pull. Warlocks were a much smoother experience, voids can tank regular mobs easily enough, and soulstone prevents corpse runs when things go sideways.

Mages can do better when dealing with magic immune mobs, just switch from frost/fire/arcane spells as needed. Warlocks are less useful here, as you mostly have Shadow, with some fire spells.