Well two main problems are: (disregarding buffs because sod can be disabled/players purged upon entering)
1. vit builds
2. determining the winner
And when you combine these two, you get a 105k hp barb sitting still and tanking the opponent for the entire duration of the fight and then, depending on how the winner gets picked, either both players get disqualified or a winner gets picked at random which defeats the entire purpose of the event.
However, I can see a possibility where an event could be established if charms and healing potions and pills were disabled, but then again mystics, mages and eps would still be able to prolong the fight endlessly, while limiting their skills would severely put them at disadvantage.