It would take like two berserkers to beat a rogue with assassinate. Against any humanoid mob, can't beat a rogue or ranger headshotting. Even non assassinate mobs, rogues would win the dps batle(in my experience). Also, rogues are much simpler to run and get good dps. Necros are the best solo class by far, but their dps needs time to ramp up and in a fast killing group, they don't hit their potential.