I've been out of contact for a week. A few things have happened since then. First, the Yankees traded for Jaime Garcia. Second, the Yankees traded for Sonny Gray. Third, the Yankees announced that Jordan Montgomery would be sent to the minor leagues to make room for Garcia and Gray. My interpretation was that
Sonny Gray is clearly a near-ace. Jaime Garcia is not. Garcia currently sports a 96 ERA+ on the season, 4.04 FIP, 4.21 xFIP, 0.305 xwOBA. He was worse a year ago, because Jaime Garcia is a below-average pitcher in the major leagues.
I began writing this post with the assumption that Jordan Montgomery is clearly better than Jaime Garcia, and was ready to write an angry reply to the veteran-biased Yankee decision-making. The data tell a different story, however. His ERA+ is a strong 114, along with a 3.96 FIP. However, his 4.37 xFIP and 0.297 xwOBA aren't much different from Garcia. He's pitched shorter outings as well, and hasn't been great lately.
There just isn't a lot of distance between Jordan Montgomery and Jaime Garcia. Montgomery's top-level stats are slightly better, while Garcia's peripherals are. They will both probably pitch about the same for the remainder of the year. Neither are on track to crack the postseason rotation. One of those players, Montgomery, can be optioned to the minor leagues, and probably has an innings limit this season.
The Yankees could, of course, convert Montgomery or Garcia to the major league bullpen. However, they don't need help in the major league bullpen. Chapman and especially Betances are mostly back on track, and Kahnle and Robertson have been great. This was on display during Montgomery's last start, where he exited the game after the 5th inning, only to have Robertson, Betances and Chapman finish the game with four scoreless innings. Montgomery or Garcia would at best be mop-up men pitching low-leverage innings. If called upon to start due to and injury, they would have to be stretched out again.
Alternatively, the Yankees could send Jordan Montgomery to Triple-A, and keep his powder dry until needed. If September rolls along and the Yankee rotation suffers no significant setbacks, Montgomery can be recalled. The Garcia move is in line with the Dodger's current rotation structure, where the team rotates 6-8 starters through the bullpen, DL, and major league rotation. They preserve his innings limit for potential need in the playoffs, and reduce the risk of future injury.