Think outside the box. I used a Voidwalker with a void fusion rifle, gear that increased the amount and reload speed of the fusions rifle, and a void rocket launcher. It wasn't that bad. Actually, it was kind of fun to see how well I could do within the restraints of the challenge criteria. It made me better at crucible overall and my scores went up upon returning to a regular loadout. I also rediscovered how fun Voidwalker can be and now switch back more, whereas I was almost exclusively Sunsinger, previously.