For the last couple of years, we have heard many a cry of the "Innings Gap", that is, the difference between the innings the Cardinals could depend on getting from their rotation, compared to the total amount of innings needed to get through the marathon of the 162 game season. Its kind of hard to believe that just two years ago, Joe Kelly was among the five Cardinals Opening Day starters, after beating out Carlos Martinez in Spring Training it what seemed at the time to be a faux competition.
Things went bad enough that the Cardinals dealt prospect James Ramsey for quite the reclamation project in Justin Masterson, who contributed little in his time as a Cardinals rental in 2014. What worked out much better of course, was the heist Mozeliak pulled on former Red Sox GM Ben Cherington, where Mo managed to get one and a half years of John Lackey for the corpse of Allen Craig and an at-the-time struggling Joe Kelly (and after a meager 2015 Kelly is back in the news, earning a rotation spot with the Red Sox).
2015 continued the chorus of the Innings Gap. This was partly fueled by trading Shelby Miller in the off-season for Jason Heyward, a move made as a band-aid after Taveras' ill-fated night. That brought Carlos Martinez into the rotation amid fears from parts of the fan base that he couldn't hold up as a starter. The team also had Michael Wacha penciled into the rotation despite suffering a very rare injury in 2014, and when he came back he wasn't the same pitcher. Jaime Garcia lurked in the shadows, as an official option should he be healthy, but by the time 2015 rolled around no one in their right mind could think of Jaime as an option.
At least by the trade deadline, things were good enough in the rotation that the Cardinals didn't make a trade for a Starting Pitcher. Garcia, Martinez, and Wacha were all pitching well at the time. They did trade Malik Collymore and Kyle Barraclough, minor prospects for Jonathon Broxton and Steve Cishek respectively, but that was more about shoring up the bullpen and giving Mike Matheny some options to avoid completely running Trevor Rosenthal, Kevin Siegrist, and Seth Maness into the ground.
Those concerns don't seem to be apparent at all in 2015. Looking at Fangraphs' depth charts, the Cardinals are currently tied for 5th in projected IP from their starters. And in fact, that's even accounting for some regression from their five Opening Day starters:
*edit: I forgot to mention that Wainwright's numbers shown here are his 2014 numbers*
The league average for GS/IP last year was 5.8, so the Cardinals five 2016 Opening Day starters got on average nearly two more outs than the average rotation per night, which adds up to a pretty big lift to the bullpen over the course of the season. That advantage is projected to be a little less than one and a half outs more than average in 2016, but you can still think of that as saving a relief appearance once every couple of games, which adds up to a lot over the course of a 162 game season.
Injuries are inevitable, especially since Jaime Garcia remains part of the five-man rotation. The Cardinals have above-replacement level options as 6th and 7th starters with the Cardinals having faith in both Tim Cooney and Marco Gonzales to step in once injuries occur. The team also has Tyler Lyons, who with no options will start the year in the bullpen, but could be stretched out as a starter if necessary. Later in the year, the hope is that either Alex Reyes or Luke Weaver would be essentially a trade deadline acquisition, which would be great because the Cardinals don't actually have to trade for them.
While the fill-ins won't project to go as deep into games as the Opening Day rotation, the Cardinals have assembled one of the deepest bullpens they've ever had. Rosenthal, Siegrist, and Maness all pitched more often than they should have last year, but now they're joined by a currently-healthy Jordan Walden Tyler Lyons, Seung Hwan Oh, and a resigned Jonathon Broxton. The depth doesn't stop there though, as the team will be able to call upon Sam Tuivailala and Miguel Socolovich when any injuries occur. This is a pen that could make up for a whole rotation of pitchers that struggle to go more than six innings, and the beauty is that they shouldn't have to.
Referencing Fangraphs' Depth Charts again, the Cardinals' bullpen ranks third in projected FIP. That gives them more credit than they deserve for playing in the NL and pitching in a pitchers ballpark, as they rank 6th in projected WAR. You might think that sells them short, since WAR is a counting stat and the Cardinals' bullpen projects as tied for 5th fewest IP, but calculating a WAR/60 IP stat for each team still leaves the Cardinals in 6th, with the Orioles dropping below but the Cubs sneaking ahead.
Of course, with pitchers, anything can happen. They break all the time, and the Cardinals could simply experience injuries in droves, leading to the Cardinals again needing to shop for at least one pitcher at the deadline. No plan that involves pitchers staying healthy is fool-proof. However, with a rotation that projects 7th best in the majors, and projects to throw the 5th most innings, and a bullpen nine legit options deep that projects as 6th best in the majors, the Cardinals are set up better than they ever have to make it through the War of Attrition that is the 162 game season.