Sonny Gray, as is presumed by all fans of the Cardinals, will be the team's ace next year. He is projected to have a 3.82 ERA, 3.92 FIP, and strike out 8.62 batters per nine innings. Fangraphs expects him to pitch 180 innings. While his ERA would be more than one point higher than it was in 2023 (2.79), his FIP is right in line with last year's statistic. Gray allowed a minute 0.39 home runs per nine innings last year; that number is sure to increase next year.
The next four pitchers according to Steamer are all within 0.5 fWAR of each other. Lance Lynn (2.3 fWAR), Kyle Gibson (2.1 fWAR), Miles Mikolas (2.0 fWAR), and Steven Matz (1.8 fWAR) would round out the rotation. Lynn gets the greatest boost in fWAR numbers due to his BABIP projections. His ERA and FIP would actually be the worst of the top-five pitchers in the rotation, but he would do a good job at limiting hits. His HR/9 ratio is a bit high for comfort, but it is in line with his career statistics.
The most interesting player out of these four to me is Steven Matz. Matz is projected to only pitch 116 innings. If he were to pitch a comparable amount of innings to the other pitchers (175 innings, for example), he would be near 2.7 fWAR in 2023, the second-best total on the staff. Steven Matz has the talent to be a #2 or #3 starter, but his health has always been a concern. Steamer projects him to pitch in twenty-nine games but only be a starter in nineteen of them.
As far as the reserve starters go, Matthew Liberatore and Michael McGreevy are figured to be the next-best pitchers. Interestingly enough, Libby is projected to pitch in thirty games this year but only start in five of them. In fifty-one innings, Steamer projects Liberatore to have a 4.05 ERA, 4.34 FIP, and strike out 8.12 batters per nine innings, good for an fWAR total of just 0.4.
Sem Robberse is included on Steamer's projections, but they expect him to start only two games and pitch a total of nine innings. I don't see him getting a chance to start for the major league team over guys who have already had a chance such as Drew Rom and Zack Thompson. It is possible he leapfrogs them or Thompson is relegated to the bullpen, but I would expect either Rom or Thompson to see starts before Robberse.