With Black Cat it's not about size either. It's a /co/ observation that the more cleavage she displays, the better a person she is. Dressed like this, Felicia was at her most selfless and heroic. Fully covered up, she was a murderous crime boss.
For Wanda, in the costume this thread is about she was the leader of the West Coast Avengers and of Force Works, and in the Perez costume she was the deputy leader of the Avengers. Fully covered up and she's just another Avenger. In her 'sensible' modern costume she isn't even on the team.