Sakura's development wasn't useless when she kicked Sasori's ass and saved Kankuro and Chiyo. Romance shouldn't be all that she's worth. I agree though that everything she did amounted to nothing at the end because she ended up with a guy who tried to kill her and her friends multiple times.
Romance shouldn't be, but it doesn't help that against sasori, and when she was saving lives, she was presented as strong and independent. The romance completely throws that to the wind because in front of Sasuke, she's weak, submissive, reserved, and shallow. By ending the way it ended, the manga showed that her character was misleading, so that development was useless.
Both.First or second part?