Trust no 1. Looking at the stats in the 2nd half of the season, unfortunately, Shota and Peterson are the better bets. I'm not blaming Shota and Peterson. They've been actually good, since the AS break. The other guys should pitch better. I hope Boyd will pitch well tomorrow.
In the 2nd half
Shota: 3.13 ERA, 3.76 xFIP
Peterson: 3.19 ERA, 3.50 xFIP
Boyd: 3.93 ERA, 4.72 xFIP
Holmes: 4.26 ERA, 4.01 xFIP
Gausman: 5.04 ERA, 3.15 xFIP
Like somebody suggested, they might need to piggyback these guys with Assad, Civale and Rea (why isn't he pitching lately?).