Usually in defender vs attacker type of games, the defender always have disadvantages of either being outnumbered or have to hold off until certain time, which is suck most of the time as average games can end much faster than the timer.
However in this game, it seems that Attacker are the one in disadvantage, they have equal numbers, no time limit, they also have objective to protect. I'm not sure who compose the game but if it's the Kaname's world GM, then it make sense he would compose a slightly advantegous rule on it.