The past two years
A Gregorius B.I.G. season?
The Didi Diamondback era began rather sooner than perhaps we'd have wanted, with injuries, first to Willie Bloomquist and then Aaron Hill, resulting in Gregorius's recall from Reno on April 16. He himself had started the season on the DL, with a right elbow strain, but had clearly recovered, depositing the first pitch he saw in a Diamondbacks uniform, over the fence in Yankee Stadium two days later. He had another spell on the DL later that month, after being hit in the head by a 93-mph fastball from the Rockies' Josh Outman [Note to Los Angeles: his actual head, not some kind of glancing ricochet, up off his back. We didn't get all huffy and start a brawl either]
When he came back however, Gregorius became our regular shortstop, starting more than three-quarters of the games for us thereafter, up until rosters expanded in September. Initially, expectations he'd be an "all glove, no hit" player were pleasantly surpassed: after 43 games and almost 200 PAs, he had a line of .307/.377/.466. However, this was partly driven by a .362 BABIP, and he hit barely above the Uecker Line the rest of the way (.206/.294/.294). Admittedly, that was also BABIP fueled (.233), but Didi's struggles against left-handed pitching were also apparent. In 120 PAs versus southpaws, he hit .200 with a .512 OPS.
Defensively, it was a bit of a mixed bag. He made some excellent plays, and there was no doubting his cannon for an arm. However, what it showed in power, was kinda missing in accuracy, and it was probable fortunate we had a Gold Glover corralling the throws on the far end. Paul Goldschmidt's 74 scoops was almost 20 more than any other first-baseman in the majors, and I suspect a lot of those came from Gregorius. Still, worth remembering he was aged 23 all of last season, making him one of the youngest regular shortstops in the majors (Jean Segura and Starlin Castro were both born the month after Didi).
There's a broad spread of projections for him in 2014, ranging from PECOTA, who dismiss Gregorius as being below replacement level, to the much more bullish Oliver system, which has our shortstop as worth over three WAR. Much of that latter optimism is due to defense, though it also projects an uptick in his power. I think we'd take a dozen home-runs from him any day, considering only eight had more than that at his position in 2013. It's not impossible, considering he hit more home-runs last year on the road than at Chase, and if he does get the job for 2014, will likely end up with more PAs, considering backup Cliff Pennington can't hit lefties either (career .601 OPS).
Presuming it is Gregorius, I think the Diamondbacks should be fine. I definitely do not think he'll be as bad as PECOTA fears, though Oliver is probably being somewhat optimistic as well. I think age is on Didi's side, and can see him, with a full season of games, producing something at least in the two WAR range. Though more than that would certainly be nice, and it is a position with clear room for the Diamondbacks to improve, over the general performance in 2013.