Heroes 6 - Discussion

The Knight has a debuff that reduces enemy damage by -7%, as well as defense by -7%, and also reduces morale and luck by -7. The debuff cannot be dispelled and lasts for 3 turns.
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What is the point of such abilities?

Well, these are racial abilities; they don't hinder making one faction more distinct from another.
In the fifth part, it was the same, only they were more interesting, as a rule: they were described more concisely, and they were just as useful.