I would enjoy seeing the take-charge, no-nonsense Wanda who is fed up with being sad all the time and wants to actually grab some happiness for herself for once. Unfortunately we didn't see that in the movie, because she wasn't acting like herself and when she finally became herself again, she went right back to being sad and sacrificing herself to do the right thing.
Basically the "you break the rules..." line was a preview of a different story, it didn't have anything to do with this movie.
For now Agatha Harkness gets to be the fun anti-hero, and we'll see when Wanda comes back whether they let her progress beyond the sad woman who screws up all the time.