New to game, did search the forums, didn't find this precise discussion, so forgive me if this is a rehash.
AoEs have been implicated as a cause of the zerg-ball tactic, and I believe measures limiting AoE damage (by capping number of targets affected) have been implemented to try to discourage zerging.
One thought that occurred to me is that it's not actually AoE damage that's the culprit - the real culprit is AoE healing and other AoE buffs/purges.
Right now, it appears that buffs/purges/heals are fairly well balanced with attacks, meaning that a zerg ball not only gets increased damage, but also increased survivability.
It seems to me that if this balance were changed so that AoE damage continues to be strong, but AoE heals/buffs/purges are weaker (or hit fewer players), this changes the dynamic. A zerg-ball could still generate a lot of damage output, but with the new balance would be much more vulnerable to getting AoE'd itself.
My thought is to keep the heals/buffs/purges strong or make them stronger in a one on one or smaller group context - the point is to limit their effectiveness in a big zerg.
I'm interested in what y'all think about this - I'm still learning the game and am not that familiar with the healing dynamic. I'm also not familiar enough with large group PvE to know how dependent on large scale AoE healing that part of the game is.