Group play is a critical, fun aspect of PvP, but it can be problematic if left unchecked. Group sizes were already adjusted before. They went from 24 to 12 players. This was necessary due to the introduction of sets and mechanics that have allowed individual players to wipe out large groups of people. So many sets and mechanics have been introduced since the group sizes dropped down to 12 people, so we are in deep need of another possible rework.
Why are large groups problematic? It isn't only the case that they can coordinate their attacks to create high burst potential. It also isn't only the case that they have unlimited DoTs. An important issue to consider is that groups make the game extremely unenjoyable for everyone on the receiving end of the stick. We can buff classes and skills as much as we want, but if regular players are faced with a large, coordinated group then they will always have a lower chance of winning. It does not matter how good we are. We will not win. This creates deep frustration among the casual community. Hardcore players should absolutely be able to enjoy the game as well. Everyone should. But we need to be able to coexist in harmony.
The only solution I see is to cut group sizes. By a lot. The reason for this is that no matter how small the group is, those people will always have an advantage over people that are not in groups. Groups have the advantage of real-time communication, which is why they can be extremely tanky and still be able to kill people with their low damage because they can time their damage accordingly and they can heal each other more efficiently. If we transitioned to smaller groups, they could keep their unlimited DoTs. Smaller groups are less intimidating for regular players to confront. This is where the game auto-balances itself. If regular players are getting abused by a small group, they could simply gather in numbers and overwhelm the small group. This is something that is NOT currently possible with 12-man groups. Current groups are more than capable of wiping out entire keeps. Simply outnumbering them does not work. They run around inside keeps, unable to be killed for unnecessarily long amounts of time, and they can stay there long after a keep has unflagged. They also hinder regular players from taking the initiative of starting groups of their own. Current large groups are elitist, to say the least, and they prevent regular players from even attempting to run a group due to the high demand in skill required to run one. Due to their large size, they also absorb much of the talent. After a group is solidified, we don't usually see those players grouping with other players. If groups were smaller, we could have more groups and therefore could increase the number of people that do group play. Large groups have become the most effective way to not only kill, but to stay alive. We need to make the solo aspect of PvP more in line with group play. We need to be able to kill players that are grouped up and we should not need half of our alliance to do so. We tried to cut group healing but reverted the change due to backlash from the large-group community. Surprise. They are not going to like any changes that will affect how they play. The vast majority of the PvP community plays either in small groups or solo. So, making changes that will tone down large groups will only benefit us all. Groups should be an asset to the larger player base, not the holy-grail of taking keeps. Let's not even talk about 12-man emperor or hammer groups.