Mages in Fates have been nerfed, particularly in Conquest because enemies have higher Resistance and Ninjas (a staple Hoshidan unit) are specifically designed as mage killers.
Hoshidan mages are also kind of gimped because Orochi has ass Speed and defenses and Hayato joins late in Birthright.
Hayato in Revelation and Ophelia in general are good though.
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More healers is hardly a bad thing