Don't blame the players, blame Bungie. They should have made the final boss count toward "mini" boss kills, and had it where it counted your teams total kills for the requirement. I do understand that if they did that then people would be afk farming the kills. So, at the very least it should count your premade fireteams kills. In the end it's pretty clear that bungie knew people would afk farm kills if they let team kills count. So they made the decision to make it only bosses you damaged count for the requirement. This unfortunately made the EAZ a toxic race to kill bosses and leave at the final boss because it's a waste of time after you get the "chests opened" requirement. Players will always use the path of least resistance. Until Bungie learns that, there will always be problems.