The big debate at shortstop for the Pirates over the last few years has been the balance between offense and defense. It's rare to get a shortstop who is good on both sides of the ball. The guys who can do that are usually star players. Most teams end up choosing between a good offensive shortstop with poor defense, or a good defensive shortstop with poor offense.
The Pirates had examples of both types of players on their 2015 roster. For the last few years they've trended on the defensive side, going with guys like Clint Barmes and Jordy Mercer as their shortstop options, despite poor offense from those guys.