The main reason why Bradford Buzzard and Black Heron considered as the show's two main antagonists because Bradford Buzzard is the one with the bigger plans and has a deep personal connection with Scrooge McDuck and if it weren't for Black Heron making Bradford's villainy to be even worse and manipulated him like a puppet (even though Bradford was already a villain) things would've happen very differently and she's more of a direct threat than Bradford (Bradford is barely a direct threat).