3 mobs isn't optimal to AoE with Quick Knock or Fire II half the time.
At low levels, you have low MP/no blizzard III and can only put in a few at a time. Sure you are doing 140% DPS on three mobs, 46.6% of Fire I x 3 but.
A healer has to heal more often; you're trading the marginal damage of a healer doing equivalent to 86% damage of Fire I. A tank has to manage enmity more (more flashes or whatever). The melee DPS/tank have to play tetris dodging if the third mob has a cone splash mechanic or an AoE circle silence mechanic. With 3 mobs and below, it's almost always better to have all 4 players focus DPSing a target down at a time and one player tab-targeting out to the next one when the mob is low HP to not waste that extra DMG.

At 8+ mobs, it is just as sub-optimal to be doing large pulls. There's a limit to how much AoE radius the skills can hit the mobs, the tank is busy spamming enmity moves with low damage / positionals to optimize AoEs / prevent party from taking damage and the healer can only put out the highest heals / regens / shields. Moderate pulls of 6 mobs seems to be the best for AoE.