Isn’t “from” redundant, since you will always be moving an item “from” the group it is already in?!
No, it’s not redundant. It’s explicitly providing information to the underlying mechanism. Could that be changed? Development would have to assess that.
The from parameter is necessary as replication allows an item to be present in multiple locations, all with the same priority. How should DEVONthink know from which of the possibility multiple equal parents it should move from?