[Neus]

The bonus damage being divided by your rounds is also a possibility. They'll both have a similar effect, but cutting the damage will result in a bigger impact, because it lowers the variance (if you somehow manage to get 4 procs of Vorpal with the reduced proc chance, it's 4x DEF, whereas if you get 4 procs of Vorpal with the reduced damage, it's the same as if you got only 1 with the way it currently works).