Also, there is quite a difference in between item collection and kills. For item trials, in an 18 person fight, one person will receive an item. Whereas for a trial requirement involving a specific number of kills, in an 18 person fight, all 18 people would receive the kill credit.
This is the whole thing though- you're not likely to fill an entire alliance with people doing the same trial (or a trial requiring the same item).

The development team needs to strongly consider reassessing how much time they want players to spend on this. Most of the game's veterans, who have bene playing a long time, are older now and cannot devote the same amount of time to the game as they did when they first started. The game needs to move away from horrible grinds, and towards content with a little more depth.