You need to do two things (if your intent is to make a "profession")
1) The internal name of your AbilityBonus school has to match the already existing ones, otherwise they are not mutually exclusive
<AbilityBonus InternalName="Champion_History">
2) If you look at the AbilityBonus in CoreAbilities.xml they will have a special tag inside them. This denotes what type they are - unit design traits, traits for champion level-ups and so on. For a profession, the abilitybonus should have this
<AbilityBonusType>Champion_History</AbilityBonusType>
If you want to make a "talent" that you can select, you should make up your own internalname for the abilitybonus (otherwise they are mutually exclusive
<AbilityBonus InternalName="Mynewthinghere">
The corresponding type
<AbilityBonusType>Champion_Talent</AbilityBonusType>
If you want to make a champion weakness, they are also mutually exclusive so you need
<AbilityBonus InternalName="Champion_Weakness">
the type
<AbilityBonusType>Champion_Talent</AbilityBonusType>
and note that your <Cost> is negative instead of positive
