Type of gear accordingly to the mage spec.
You already gave a good example: you specialized on battle mage? You unlock the ability to wear chain mail armor through that skill tree.
That way you evade full casters wearing heavy armor and other random combinations.
Depending on the role the mage will have: Cloth for dps, Chain mail for tank and cloth for healer.
Mage are known to be a control or smart class with low survivability. Use to be a ranged class.