On the way to the Bronze 3 Stars monster zone, Leo was actually quite disappointed with the amount of Exp he received.
Before Bronze 3 Stars monsters earned him an average of 250 experience points, while now they were only yielding 20 points. Considering that the Experience points were being shared by 5 people, Leo would receive a maximum of 100 points if he was hunting alone.
On the other hand, Leo noticed a very good change that happened to him.
Since he rose to Bronze 4 Stars, the ease with which he hunted monsters had gotten a lot greater.
Leo realized that if he didn't need to run to get the arrow after killing the monster, he could kill hundreds of monsters a day.
So by stepping up to Bronze 4 Stars, what he lost in the quality of experience he could get for each monster, he can make up for it with the amount of Experience he gets for killing a lot more monsters in the same amount of time.