In Stormblood, the DoH Class quests had the materials provided for you (similar to DoH Tribal quests), allowing you to focus on your gear and rotation, and if you mess up, just ask for more materials. Meanwhile, the DoH Role quests in ShB and EW are more like the Custom Delivery system, which wouldn't be a problem except that you can't buy the materials from a vendor like you can with Custom Deliveries, you have to either gather them or (if you have none of your DoL at a similar level) turn to the Market Board, of which the prices can get fairly high. Basically, I don't know why they changed the system.