I remember the first version of the rules, when some were still building the Capitol :D. Back then, all magic specialists were limited to level 4, and Tanta was banned (even on Xiron))), because she was considered overpowered. Then the skill level increased, and people started saying that it didn't matter anymore, because warriors were still better, and so on. The bans were removed. Now the skill level has increased even more, but it seems that bans are relevant again :D
These bans (or some other decisions that prevent such specialists from getting a mega boost) are relevant specifically for mirror matchups when playing without anti-magic artifacts.