You misunderstood the system For the triumph and the emblem of it you have to complete every mission on Legendary, no matter on what character For the 1520 Armor and the Exotic you have to complete each mission on Legendary on the respective character You have not played "The Ghosts"and "The Investigation" on Legendary on Titan This mission should have a red icon on the far left of the modifiers when you select it This symbol indicates whether you have already played this mission on Legendary on this character or not So play all missions that still have this modifier and you'll get your Exotic