Why do you think she is a waste? I think she is worthy of being a kage if something ever happened to Naruto or Sasuke. They would have never achieved such high status if it were not for her. She saved Naruto with her med jutsu and gave Obito enough chakra to open Kaguya's dimension and save Sasuke. So she's not the greatest fighter ever but you at least have to respect her strength and she's probably improved a lot more since the time skip. Between Hinata and Sakura its a coin flip for who would be the best hokage I wouldn't mind either way.
Her feats in the final moments of the manga were forced. Kishi only wrote it to sell the message of "friendship" and "team 7 forever!"
If you do a bit of storytelling, you would know a lot of mistakes did. Sakura had many motivations that clashed with her actions. She keeps reverting back to "saving" Sasuke. If you want to know the most sensible route for her character you only need to look at Ino.
Ino is Sakura would have been if she were written sensibly. By sensibly, I mean her actions are based on her motivations and her motivations did not go back and forth. Naruto and Sasuke did suffer this forced narrative but not on the scale as Sakura.
Just because you see potential on Sakura does not mean she is a great character. As well as being able to do incredible things due to Deus Ex Machina does not make her a powerful character.
You might as well go "Because she/he can" whenever there was an asspull.
For example, "how did Sakura even survive her bout with Kaguya?"
Kakashi and Obito can and even that was a stretch but for Sakura? Almost nothing can answer that question and be satisfactory. The only thing that can even get close is because of the Byakugou. That means that even if it was not all Deus Ex Machina, at best, her survivability is dictated by as long as she can keep the Byakugou active and that run time is not that long.