They need to make it so that after you reach level 50, all dungeons grant a small number of the DL related tomes when running them with a first timer, as well as added bonuses for running 100% completion. Preforming tasks could contribute to the overall grade, examples being opening all the treasure chests, killing all the enemies, and using a certain mechanic against a boss (Sastasha: blocking at least one wave of adds from popping by interacting with the bubbles, Toto-Rak = destroying the tail on the mega boss, etc.) These tasks could be displayed on the duty list when you enter a dungeon, and be checked off as you complete them. And if you reach 100%, getting an S rank, you get a silver treasure chest with contents from an earlier boss in the dungeon.