When someone writes a cathartic story about Diamond, its entire premise centers around her downfall. The intent is to make her defeat as humiliatingly satisfying as possible, and doing so requires justification. Therefore, the author will attempt to do everything in his or her power to build Diamond up enough to justify her defeat: Embellishing her rudeness, having her cross the moral event horizon, giving her loathsome qualities that society disparages, and even going so far as to increase her threat level by giving her evil powers and having her take over Ponyville. That way, no one feels bad when she slips on a bar of soap into a large puddle of mud in front of the entire town, and everyone laughs at her as the hero honorably shoves the same soap into her mouth before she can protest. And then she gets forced to work at Sweet Apple Acres as punishment.
 
It’s interesting that this sort of sleight-of-hand technique arises in the creation process despite the reason for the story being so emotionally driven. Anger may cloud people’s logic, but it certainly doesn’t outright remove it.