In 2014, only five teams had a worse defensive middle infield than the Miami Marlins. Adeiny Hechavarria was supposed to be a glove-first shortstop, and pairing him with Dee Gordon, a converted shortstop playing second base, in 2015 was an opportunity to improve -- which they did and then some. In 2015, only one team had a better defensive middle infield than the Marlins. The turnaround was remarkable, and the biggest in the big leagues last year. The reasons behind the turnaround were ... less remarkable.
It's not that there weren't adjustments, they just seem so simple.