the main cause of poor WvW performance is the game trying to load cosmetic for the opposing team in real time, since the game can't know who will show up and preload the skin. to stop this, simply set opposing team to use "default model". this problem will get worst as anet add more skin! 😃 if that still doesn't help, your only option is to reduce the number of player the game display which has a negative impact on experience.