Since the middle of 2009, the Cardinals’ left fielder has been Matt Holliday. Injuries kept Holliday from playing a full season each of the last two years. For that reason and perhaps others, the team decided not to exercise his $17 million option, instead paying a $1 million buyout. Similarly, the team opted not to give a qualifying offer to Brandon Moss, who hit 28 homers but also struck out 30% of the time, somewhat limiting his value offensively. As a result, the Cardinals entered the offseason with two starting outfielders, Randal Grichuk and Stephen Piscotty, and a hole. Following Ian Desmond’s deal for $70 million with Colorado and the White Sox’ trade of Adam Eaton to Washington in return for major package of prospects, the Cardinals elected to fill that hole with Dexter Fowler on five-year contract worth $82.5 million.

Fowler is coming off the best campaign of his career, having slashed .276/.393/.447 and produced a 129 wRC+ for the Cubs while recording average defensive numbers in center field. The result: nearly a five-win season. Fowler’s best attribute on offense has been his ability to get on base. He has a career walk rate at 13%, and of active players with at least 2,000 plate appearances, only Paul Goldschmidt, Bryce Harper, Carlos Santana, Mike Trout, Jose Bautista, and Joey Votto have walked more frequently. He has generally been a high-BABIP player, only once (2015) recording a mark lower than .320. He doesn’t steal a lot, but he does so with an acceptable success rate, has hit double figures in every big-league season, and has posted good baserunning numbers throughout his career.

His success getting on base will make him an ideal fit for St. Louis, who have been itching to move Matt Carpenter down the order since Carpenter’s power surge in 2015. The team tried to shoehorn some players who weren’t good fits occasionally last season, but Fowler’s numbers profile well in the leadoff spot. Fowler should also help the Cardinals’ baserunning, which was awful last season. Also ideal for the Cardinals is Fowler’s aging profile. This deal will take Fowler through his age-35 season. Fortunately for St. Louis, Fowler’ skills at the plate should age pretty well. I looked for Fowler comps when I profiled him earlier in the offseason, and I found that hitters like Fowler have historically recorded a 110 wRC+ from ages 31-34.

Whether this turns out to be a good deal for the Cardinals isn’t likely to depend on Fowler’s bat, but his glove. The Cardinals wanted to find a center fielder capable of moving Randal Grichuk to a corner-outfield spot and improving the team’s defense. Fowler should improve the club’s outfield defense relative to the 2016 season, but there’s considerable debate over how well Fowler’s glove profiles in center field. Fowler’s defensive numbers in Colorado and Houston were pretty terrible; the last two seasons in Chicago, on the other hand, they’ve been close to average. Generally speaking, using three years of defensive numbers will give you the best idea of a player’s defensive talent level, but there has been a strong narrative to Fowler’s improved positioning helping him get to a lot more plays in the outfield.

I have written about Fowler’s defense on multiple occasions, but it’s relevant once again today. How Fowler’s defense is assessed changes his value as a player significantly. If Fowler proves to be a bad defensive center fielder for St. Louis, like 10 runs worse than average per year, then he’s a $50 million player over the life of his contract (with standard aging–if he ages well, he’s at about $70 million). If he’s a slightly below-average defensive center fielder, he’s worth the $90 million (including the value of the lost draft pick) the Cardinals are paying him. If he’s slightly below average on defense but also ages well, like his profile suggests he should, then his value is in excess of $100 million.

While the capacity to estimate defensive talent using publicly available information has improved, the sample size required to make good determinations is still quite large. As a result, it can be very difficult to determine the causes of improved defensive numbers, which could be the result of variance in a small sample or a real change in talent or better positioning. We want to believe in a narrative. Finding numbers that back up a narrative is tempting, but the truth is a bit murkier.

This isn’t merely the case for Dexter Fowler. Adam Eaton, who was a potential alternative acquisition for the Cardinals, poses similar challenges. Eaton’s numbers in center field don’t look a lot different from Fowler’s. Eaton is three years younger, but his value offensively has been roughly similar to Fowler’s over the course of their respective careers. In order to pay around $50 million for Eaton’s age-28 through age-32 seasons, the Washington Nationals had to give up roughly the equivalent of Alex Reyes, Luke Weaver, and a third piece. The Cardinals opted to pay an extra $40 million, keep Reyes and Weaver, and sign the slightly older version of Eaton in Fowler.

Presumably, the Cardinals scoured the trade market, and didn’t like what they found. Lorenzo Cain, Marcell Ozuna, and A.J. Pollock likely would have had more impact in 2017, while players like Charlie Blackmon and Jarrod Dyson have also reportedly been made available. Given what we know of the available options, there’s some sense to the Fowler deal. The problem with it, though, is that it doesn’t really move the needle for the team. Before signing Fowler, they were likely to be competing for the Wild Card with the Giants, Mets, Marlins, and Pirates. The extra game or two Fowler provides for them them could prove very important for a team that missed the playoffs by one game last season. When it comes to the division, though, there’s still a 10-game gap between the Chicago Cubs and the St. Louis Cardinals.

After signing Brett Cecil to stabilize the bullpen and Fowler to stabilize the outfield, the Cardinals are a team without any holes. Their worst position player is Jhonny Peralta, and he’s pretty close to average. That’s a good thing. But their best position player is Matt Carpenter, and he’s likely a three-win player. On the position-player side, the Cardinals are completely lacking in star talent, true difference-makers who could help close the gap between the division rivals.

On the pitching side, Carlos Martinez could take another step forward and establish himself as an ace and Alex Reyes has that type of potential, as well, but they don’t have anyone on the position-player side who possesses that sort of upside. The Cardinals thought they had a future star in Oscar Taveras. Then they thought they had one in Jason Heyward. Dexter Fowler isn’t in that class. The Cardinals could sign another free agent like Edwin Encarnacion or Justin Turner now that they’ve already lost their first-round pick, and that could get them closer to the Cubs, but if they’re going to catch the best team in baseball, they’re going to have to find a star somewhere. The Cardinals were going to be good with or without Dexter Fowler, and Fowler fills some of the Cardinals needs, improving them for next year, but he isn’t going to make the Cardinals great.