When pvp happens on a populated server. The chance you will be fighting groups versus groups is higher. So if you wipe a group your pvp quest is ready for turn in. But who wants to stop pvp to turn in a pvp quest.
My suggestion is to either bump the number to 10 kills. Or have the option to have a 10 kill quest. Possibly buying it with faction points. But also having double the rewards. If that doesn’t work, when.you kill 5 you have an automatic turn in with s popup option to continue another 5 kill quest. You would be able to continue pvping without losing out on pvp fation points.