Eh, that runner was on first base, it was arguably the slowest player on the team, and there were two outs. It would've taken at least two hits (off Siegrest no less) for Ross to score. With the lead, I think run prevention remains the most important factor, and to me, an Arrieta who didn't throw 120+ pitches his previous outing takes that AB and is the best option for the 8th inning.