Guild requirements for these events are weird because the game hides data (like “number of sigils spent”) that is useful for tracking it. The devs asked for feedback about what they could do to improve it, then never spoke about it again. (Any news on that, @Cyrup, @Saltypatra?)
So a person who got to boss level 90 with 400 points could be a low-level newbie who tried really hard and spent 500 sigils with a ton of losses, or they could be some high-level deadbeat who slapped a team together and ground out 0 tiers worth of sigils with no concern for strategy. You sort of have to feel your way through it, ask the high performers what they spent and how they did, then pick a watermark that “looks like” what the requirements should’ve accomplished.
That said, I fight really hard to try and be in my guild’s top 10 every week. I got my ass kicked this week, with more losses than any other event I’ve played. It’s demoralizing to be at this phase of the game, have people depend on you, and fail so hard.