Batting sixth: RF Kerry Carpenter
Kerry Carpenter had an excellent offensive year and a less excellent defensive one, where he spent most of his time in right field. Putting him in the outfield in the dream lineup instead of moving him to DH full-time (which is probably what will happen in real life, given Miguel Cabrera's retirement) is purely an accommodation for Shohei Ohtani, who has a short history of playing in the outfield but not enough of one to put him there everyday, especially after a major surgery.
Carpenter's inclusion here does come at the expense of OF/3B Matt Vierling, who also had a productive offensive year and appeared in all corners of the outfield throughout the season. Carpenter and Vierling have relatively comparable offensive numbers: Carpenter hit .278/.340/.471 with 20 home runs and 64 RBI; Vierling hit .261/.329/.388 with 10 home runs and 44 RBI, but with more hits for extra bases.
It's the differences in those numbers that come out in Carpenter's favor, even if his performance in the outfield can be a little nebulous. It could be a position and lineup spot that would fluctuate a bit during this fictional season, with Carpenter in the role more if he can step up defensively, or Vierling if he can step up offensively.