How to Beat It
More easily than you think!
Play elementalist. Take all 3 beams (you start with lightning, so pick up arcane and light), and Call Lightning, and then 2 buff spells (either Arcane Power or Bloodlust, and Might for the second). Step 3: Profit.
Honestly once you get past the first loop your damage and area will be so high that the only worries are ground aoes that enemies manage to cast before they die. Bosses were melting in seconds.
Also of note, having the Purity, Focus Fire, and Generalist runes helps a TONNNNN because of the damage multipliers (they are multiplicative instead of additive like most damage bonuses).