Forgive me for being a little circular, but the Cardinals' good starting pitching depth is very good for the Cardinals. Less clear is whether that depth is beneficial for the development of all eight potential starters. Heading to the offseason with upgrades needed at shortstop and potentially centerfield, a trade seemed like a legitimate possibility. The Cardinals instead traded for Peter Bourjos and signed Jhonny Peralta to a free agent contract. That left the Cardinals with no major league holes, and no immediate reason to trade one of its pitchers.
Based on service time and ceiling, the two pitchers most likely to go in a non-blockbuster deal are Lance Lynn and Joe Kelly. For their careers, a trade might be the best thing for them if it guarantees a rotation spot. Putting a rookie in the bullpen for a year to get used to major league pitching is a very effective strategy for young pitchers to adapt to big league hitting. Putting a pitcher in the bullpen after a couple years of starting often ends a pitcher's tenure as a starter.
Given good health, the Cardinals appear prepared to go into the season with Adam Wainwright, Shelby Miller, Michael Wacha, and Jaime Garcia. Trevor Rosenthal would have been a candidate for the fifth spot, but is now the closer. That leaves Lance Lynn, Joe Kelly, and Carlos Martinez for the fifth spot in the rotation. For 2014 only, an argument can be made for any one of the three pitchers, with each capable of moving to the bullpen if necessary. Of the three, Carlos Martinez has the highest ceiling and is the only one capable of becoming an ace or number two starter. Given the projections for the rest of the rotation and bullpen, Martinez could be allowed to struggle without impacting divisional aspirations. If there is no such thing as a pitching prospect Martinez might be one of the Cardinals' best starters already. However, leaving him in the bullpen for a year would still serve to aid his development as a pitcher, and is very likely the path of least resistance.
As for Lynn and Kelly, at least one of them is likely to start the season in the bullpen. Whether fair or not, whoever ends up in the bullpen will lose important developmental time in the majors. Each has shown the ability to get outs as a reliever already, and putting them back in the bullpen, while beneficial for the Cardinals is not the best move for their careers. With Miller, Wacha, Martinez, and Rosenthal in the fold, it is easy to forget that Lynn is just 26 years old, has started only two years in the majors, drastically adjusted his body-type before last season, and has shown signs of wearing down in each of the previous two seasons. Joe Kelly is only 25, has made only 31 starts in his career, and has not yet figured out how to strike guys out as a starter despite throwing 95 miles per hour.
For 2014, Kelly and Lynn are more valuable to the Cardinals as back end starters, bullpen help or insurance should someone ahead of them go down. Unfortunately for them, their careers might be better served taking the mound every fifth day to cement their status as members of a big league rotation. The benefits of pitching on a winning team should not be understated, but the unintended consequence of the Cardinals' great pitching depth might be slowing a couple young pitchers from reaching their potential.