Marauder dps

I am playing witch atm, seeing how many crit and dmg nodes it has while lacking any kind of damage mitigation makes me think witch is supposed to be a glass cannon with insane dps. Currently i have 800 dps on my main aoe spell, but there are insane dps witches with like 1600 dps on main aoe spells (you may not believe but its very possible).
I wonder how much damage big tough guys do having mostly those lots of defensive nodes. Can you achieve at least 300 dps for main aoe skill, Or do you only tank and rely on others to kill things for you?