Speaking from a MCH PoV here, I adore Arrow anytime I am using my burst combos with Wildfire. Usually with Arrow active, I can get in a near full combo a third time, if not half a combo without rapid/proccing. Either way it increases the overall damage of that burst string usually around 2-3k on its explosion, more if random crits are feeling generous. When you spot a MCH throw out Wildfire (look for the red smoke and the little red beeping bomb to appear on boss), it's a perfect time to throw it their way then.