Unfortunately, ONLY nades and barrier melee count towards the kill. Kills with weapons of light or blessings don't count, nor do kills while barrier is active count either. However, you can get this part of the quest done significantly quicker than normal if you load up the 'Lost to light' mission, any difficulty is fine. Do the mission normally until you get to the room with 3 locks. Pick up a tomb husk, and you can melee everything to death since for some reason, you have unlimited melee while you are holding a tomb husk. Once you have killed everything in the room, kill yourself with a nade or something. Rinse and repeat.