Unfortunately I think it’s easy to confuse a shitty character with shitty writing, and that doesn’t make Sakura useless - yeah, you could say it’s a result of the shonen genre that she doesn’t get any screentime, but that doesn’t mean she’s not an important character.
Disregarding her status as one of, if not the most proficient healer in Konoha, and that Shizune herself has said that Sakura’s surpassed her, and that Sakura took down an S-rank member of the akatsuki - In this arc alone she’s both cut open Naruto to restart his heart and used the chakra from her Strength of a Hundred seal to help Obito in rescuing Sasuke from the other dimension. She saved both their lives. Without Sakura the two big shonen protagonists would be straight-up dead. I wouldn’t exactly say that’s useless