Get in a fire team with friends who can actually help bring a bunch of mobs low, but not kill them so you can finish them off for max orbs. I had an Alpha Lupi chest too for the extra orb which may help. Wiping doesn't reset the counter too, so if you find an easy spot with many adds do it there. I completed the striker at the staircase gauntlet in Undying Mind strike. Didn't care about the 220 mark I received but was happy to finish the quest.