The thing is, all 3Bman are graded the same way on fangraphs, and the plus or minus scores are comps to other 3Bmen. His range compared well with other 3Bman, and yes I can "compare." His throwing and DP tries compared very badly, and he made more errors than almost all 3Bmen- many on throws.
I did not see the same things you did. I actually thought Devers looked pretty quick at 3B. On the few times a 3Bman has to run to catch a pop up, he looked okay, to me.
He made a few really nice plays, but not as many as others.
It seemed to me, he made more throwing errors than most 3Bman, but I'm not sure the numbers back up my perception on that. We all know he made a lot of bad throws- many to 2B on DP tries.
He was one of the worst defensive 3Bmen in MLB. I've agreed with that for years. Without a bad arm, he might have been around 20th to 24th out of 30. That could easily translate to 12th to 18th at 1B, overall, as throwing is not a major component of 1B D.
The other thing I repeatedly brought up was that the bar was set low by Casas, and all he had to do was be equal or better than the worst 1Bman in MLB to move from 3B to 1B and have it not hurt us.
I feel he'd be better than the worst 1Bman. I think he could be around 15th, over time. There are some bad 1Bman in MLB. I'm fine if you disagree.
BTW, my choice is Campbell at 1B, Devers at DH FT and forever, and Mayer called up.