What?! How is that even a valid argument? If you were actually FIGHTING over the kill then I would agree. But there is no fighting. If even ONE extra person attacks the boss outside of your raid group the boss will insta kill everyone. That makes absolutely no sense no matter how you look at it. The only people who benefit from this feature are trolls and griefers who have nothing better to do.
As the last person said ... deal with it. Our guild has tremendous fun with the boss every week. Many guilds compete over the kill, both Reps and Imps, sometimes we sabotage others, sometimes they do that with us, we almost always end up being victorious. This reset it was hilarious - one bad Imp guild couldn't kill it due to enrages/dps being crappy, so while they were recovering, we quickly pulled and killed it. We even had some Reps sabotaging our healer group.
In other words, please do not listen to whiners, it's just ONE boss, it isn't even necessary to kill if you want the best gear, tbh. There's plenty of instanced bosses, Piligrim is just ONE. If you can't deal with its issues, don't do it, it's as simple as that.