Fuji and gb couldn't catch sabo, what makes you think fuji could 1 shot zoro who tanked an acoc combo attack from both bm and kaido that was intended to kill the 5 worst generation members involved in roofpiece.
I agree that fuji didn't go all out because he didn't try to help luffy beat doffy, but if he could have broken the birdcage without attacking doffy he would have, at that point zoro hadn't unlocked his conquers haki, if he had he would have been able to cut through the birdcage but instead they all had to work together to keep from getting chopped to bits while waiting on luffy to win