I suppose it depends on what you mean by disappoint and what your expectations are for each player. Smart is already a quality NBA player but not an all-star level player, nor do I think he is likely to become one unless he can improve his shooting. If you were expecting him to be an all-star you might find him disappointing. If your expectations were more measured, then you might not. Brown has done better than many expected in his first year, but there is still a lot of growing to do, the jury is still out. In a way you could make a case that Tatum is the most likely to disappoint precisely because the expectations are so high. If he becomes a pretty good, but not special player many would be quite disappointed.