At first I thought that single class Evoker would be better for the higher power levels and spells, but it still wasn't impressing me on its own.
Then I made him a nature godlike and multiclassed in Berserker, the int debuff sucks, and I can't cast some spells without worrying about my team. However the action speed reaaallly helped with the increased cast times, the might buff added more damage than power levels, and most importantly was the penetration. Biggest problem I had with wizards was a high enough armor enemy just shrugging off all my spells, the berserkers +2 penetration applies to everything, including my spells, it Reallly made the difference and suddenly almost nothing had better armor than I had pen. He easily did the damage of the rest of my team, combined. Near the end I was basically solo running until last boss through sheer damage.