There is an important disanalogy here. “Black” in this context is synonymous with “African American“, which refers to a particular culture with a unique character and history. “White“ is a catchall term that refers to a variety of different cultures who really don’t share much of anything. The only reason to use the word “white“ this way is to make reference to the social structures that enable racism. That’s why the emotional impact of “white girl magic“ is so different from “black girl magic”. I don’t think most people would have trouble with a phrase like “Irish girl magic“ or “Swedish girl magic“. would you?