This all reminds me: A good enough Minion Master, like a Necromancer type, can completely outperform a Tank quite often. While a proper Tank build in most MMOs can take a lot more damage than the average throwaway minion, it is usually a lot easier to control aggro with a cluster of multiple minions and even bodily obstruct enemies by crowding around them. Plus particularly with Necromancer type MMs, they tend to excel at battles of attrition since every dead enemy further empowers the Necro.
It was just a random thought. That a team-mate drawing too much aggro from the Tank with their high damage output wouldn't necessarily have the same problem with a Minion Master set-up.