From what I've seen of Julia, she is quite impressive at such a young age. What is she, 13? Will she survive adolescence with her skating skills intact - that is the question. At least Gracie is all grown up, her big challenge is to improve her artistry and presentation skills.
We do not know that so it's pointless to wonder; better to just enjoy the skaters as they are. At this point in time, Julia is a better spinner and has better presentation skills.