Looking at two mage regiments dealing physical damage, Two-Skull's Gang and Necro-Anup Cult, makes you think that Two-Skull's Gang is definitely the better regiment. But the average values for Two-Skull's Gang can be lower than those of Necro-Anup Cult in the whole spectrum, for example. Also, both regiments have completely different sets of abilities that must be considered for this equation. And most importantly, you have to remember about the impact of terrain bonuses and equipment in combat! Differences between classes are only one part of several battle factors.