Harris is a luxury pick. RBs tend to get dinged, having a Bama bell-cow, who is a monster pass blocker, sitting behind glass in case of emergency, is nothing to sneeze at. Rb is fairly plug and play, and the kid can do it all. Some predraft venues had him ranked as the 2nd back behind his teammate Josh Jacobs. Others had him around 5. He was the 6th back taken, after a bit if a run on em early in the 3rd.
White isnt getting younger, Rex is a vet (we dont pay vet rbs often), and Sony does have a concerning knee issue. An insurance pick at RB seems more than reasonable.