In this setup, I think the easiest way to catch up here is to use a standard issue Ubercharging/missile storm build.
While the God spellcasting options have more kick and synergise better with the group, they also require a greater degree of tactical skill to place battlefield control effects where they hinder the enemy without screwing up allies.
Ubercharging is simply point and click, if you can reach them they die. Nothing fancy there, just a 2-handed weapon, and as many multipliers and adders to damage as you can get onto it.
Archery on the other hand, simply aims to hit a bajillion times with fistfuls of bonus damage sources, it might be easier to counter(though with your group I doubt Wind Wall or lousy weather would be a problem), and hits less hard, but it does get tactically easier to pull off without shoving yourself into a potential meat grinder.