Darius' Luck manifested itself in easy critical hits. It seemed like whenever he sprayed his spell around, it would strike the weak points of the monsters someway somehow, through some bizarre spot of… luck.
Darius felt reassured that allocating points in that stat had been the best possible choice he could make just seeing its effect in battle. In about 3 minutes, the duo of Gunner and Darius had cleared out the monsters within this cavern, being granted their loot as they did so.
As for the post-battle report…
[You have gained 15 EXP, 10 Bloodleaf, 13 Andir Fruits, 4 Indigo Sap, etc.]
[Gunner has gained 15 EXP, 5 High Fibro, 9 Kisu Stem, 7 Forest Essence, etc.]
Clearly, higher levels equaled low exp gain. In fact, both Darius and Gunner were lucky that these foes were within the 5 level boundary. Otherwise, forget 1 exp point, they would have to swallow a big fat nothing for their efforts.