It appears to be a problem with

<EquipmentUpgradeDef>

<EquipmentSlot>Weapon</EquipmentSlot>   

<EquipmentWeaponType>Staff</EquipmentWeaponType>    

<EquipmentSlot>Defense</EquipmentSlot>    

<SelectionCriteria>MaximizeSum</SelectionCriteria>    

<ComparisonAttribute>UnitStat_Attack_Cold</ComparisonAttribute>   

</EquipmentUpgradeDef>

I commented this out and I now get the Mages showing up.

To fix the problem I found the following works.

Change

<SelectionCriteria>MaximizeSum</SelectionCriteria>

To

<SelectionCriteria>MaximizeBest</SelectionCriteria>

and add the line to the equipment defs

<ForUpgradeActionOnly>1</ForUpgradeActionOnly>