While I don't think she's useless character-wise or strength-wise, the narrative, and Kishimoto himself, makes her seem useless. Even back in Part 1, every time there was a fight, what did Sakura do? She sat and watched. If I had a dollar for every time I've heard "Sakura, get behind me" or "Sakura, stand over there" or "Sakura, stay back", I'd be a god damn billionaire. It's ridiculous.
And even in the latest chapters of the manga, all she does is get saved. She tries to do something, fails, and has to be saved by Naruto or Kakashi (because Sasuke is too busy being an a*****e to save anyone).
She could be useful, but Kishi refuses to have her do anything meaningful. The worst one is when she tries to kill Sasuke. She's right there. Literally inches from his back. And what does she do? She chokes up, and has to get saved. Again. By Naruto.