This feels correct to me. Luis Arraez is not a huge, lumbering guy but his sprint speed is the 36th percentile (Sano is 39th percentile by comparison). Arraez is a slow dude and I suspect that hurts him a lot more at second base than it does third.
Of course, his arm also isn't very good, which doesn't help his case at third. Either way, if he's going to play a position for the Twins in 2021, I'd like to see him get a lot of reps at third base, which lets Gordon also get a lot more reps.*
*all of this assumes Josh Donaldson will remain perpetually injured