I think the Diadem only needs two changes. 1) not allowing gatherers to roll on gear. 2) if someone (on their battle class) did not contribute then they don't get an option to roll on loot.

I think aggro should calculate contribution. I'm not suggesting people should have to get a large amount of aggro, just a small amount to show they were there, helping in some sort of way. By doing it by aggro, healers wont get punished if they need to save someone instead of hitting a mob(so they don't choose to let someone die in order to get loot), etc. Aggro doesn't count towards getting a chest, but again, I think it should be able to calculate if someone can roll on loot. None of my suggestions are out of spite. I only want a better experience.