I have never been able to understand the "I can totally do the thing I've been committing fraud claiming to do, despite never once actually doing it, because I'm prettier than the actual genius doing it" trope. I know its to set up the arrogant person for a failure, but its just so far beyond arrogant that it doesn't even feel sensible for a story. Imagine a modern story where the evil sister says "Yeah, I can totally design a state of the art space shuttle despite my C in Engineering 101. After all, my sister the world renowned rocket scientist has been designing space shuttles widely regarded as the greatest in the world, and I have nicer hair than her."