A random thought from someone who had yet to play a game, rather than a serious suggestion, but has anyone considered awarding experience points for each member of their own warband who has been killed by magic?
If the main aim of each wizard is the pursuit of knowledge, then observing the effect of enemy spells on one's own hirelings should count for something (though not as much as casting the spells yourself obviously).
Might this go some way in countering any perceived imbalance when playing against more 'killy' wizards?