The faction class items are glitched for the exotic class item quests You need to use a spektar class item from the chroma packages or a year 3 faction class item that has a vanguard rep boost (not one with a crucible rep boost) I did 2 since RoI. For one I used a spektar class item and I used the year 3 class item with vanguard rep boost for the other so I know this works When you get a new faction class item, put on your gear and take it out on patrol. Kill a few dregs or something and see if you get some progress on the "kill minions of darkness". It's a lot better to see if it works this way than grinding out a load of strikes or pvp and then seeing that it's not working