Sakura isn't useless.
She is good medical ninja, and has shown that she is passable at taijutsu. Combined with her monster strength she might as well be called a taijutsu specialist since she only needs to land one hit.
As for the whole Sasori debate, she deserves no credit whatsoever as an individual. Had she gone 1 on 1 with him she would have been curb stomped. Chiyo going one on one with him probably would have done herself proud before getting killed.
And in the end Sasori pretty much killed himself anyways.
That is all.