Going to say, a striker titan is just as effective as a defender here. On atheon, whenever I go in I use fist of havoc with death from above (helm of inward light) and shockwave to kill the enemies. That way, the relic person can focus on keeping us cleansed, and so he doesn't get killed by the enemies. Though defender gives void damage, you can make it up with a void fusion rifle and machine gun. Your fusion rifle doesn't have to be legendary to be good in there. I use a rare just because it has a moderate impact and a fantastic charge rate. The faster you can get your shots out, the better