There are a few problems with using Eaton in the 2 hole.
First, he's not nearly as good of a hitter as Moncada, assuming Moncada returns to 2019 form. You don't give extra ABs to worse hitters.
Second, he's a platoon hitter, at least part of the time, vulnerable to lefty relievers. Moncada is a switch hitter, able to handle whatever reliever is thrown at him in the late innings.
Third, Eaton can be a good hit and run player, both behind Robert, but more importantly, ahead of Madrigal. You don't want to hit and run with Abreu behind you. You don't want to try to steal ahead of Abreu when it might result in an out. If you do it in front of Madrigal, you turn him into an RBI guy with just a single, and if you end the inning with an out, Madrigal is a fine lead off hitter for the next inning.
Fourth, by grouping Robert, Eaton/Engel, Madrigal at the bottom, followed by Anderson, gives the Sox their speed together with no one to clog the bases between them. I think LaRussa will use that speed to put pressure on opposing pitchers and produce more small-ball runs than we did last year.