This is a slippery slope though.
Its better when these types of effects happen on a level of class mechanis, because this way they work locally in specific engagements, rather that affecting PvP balance globally in the whole zone, even if its a 6man hunting solo players.
A simple example of such mechanic is the difference in target caps between group heals and AoE attacks - one only hits up to 6 targets, while other up to 24, meaning AoE heals scale up with ally numbers worse than AoE attacks scale up with enemy numbers.
Another example is Slayer's Even the Odds ability, which gives stronger buff the more enemies yout hit, which in principle means that a smaller group will get more benefit vs a larger group than vice versa (ignoring the fact that in the current state the ability is nearly worthless and is capped at only 9 targets)
At the same time healing effects that can heal out-of group with high target caps play directly into supporting zergy groups.