One of the best ways Rizzo could have improved the team woutd have been to drop Morgan, as soon as possible after the end of the season, and replaced him with a "frontline" centerfielder and trade for him, if he had to.
There is no greater detriment to this team getting better, based on his play and behavior, than Nyjer Morgan. Subtracting Morgan and adding a top centerfielder would have been a big plus, ie taking away a big negative and adding a big positive. Hell, just getting rid of Morgan is addition by subtraction.