Not sure if anyone actually thought of this but why not just provide a very sweet incentive for teaming up if you're grinding in the same Zone.

Like for example:

If a player in a Guild, parties up with someone not in thier Guild, Alliance Guilds or no Guild they and the other person(s) will get a 125% increase in drop rate for each individuals in the group. With a full party that will add a 500% drop increase applied to all in the party.

If in the same Guild or part of their Guild Alliances a 40% increase in drop rate should be applied for each one in the party. To prevent abuse of this system so that guildmates dont just leave their Guild team up and rejoin the guild the 40% should also be applied if two or more people in the party are not in a Guild. And to prevent AFKers the drop rate buff should only be applied to the mobs they hit so if they don't hit anything cause they want to leech they'll get the regular lame drop rate.

The cool thing about this idea is that it can mix, like for example if there are two guild mates already in a group and they add a random person who isn't in the same guild or not in a guild, each person will benefit from a 205% drop rate increase [Guildmate(40%) + Guildmate(40%) + Random person (125%) = 205% drop rate].

This boost in drop rate will make people more willing to add a random person rather then just killing them for just existing in the same area and prevent people from deliberately reviving and dying from the same person over and over again in order to get

them to leave.