I don't get what people mean as a mistake. Even if we look at him as pessimistically as possible, he's still way better than anyone we had off the bench last year. Furthermore, even on his worst nights, he still can pull out opposing centers and open things up in the middle like Rodney Rogers did when he was here. On his best nights, he can score down low, defend, and decimate teams from the outside.
I don't know what people were expecting from him, but he's still one of the better bench big men in the league and he will get hot again and make everyone forget about the past few weeks.