Allen has been checking down to the backs a lot this year, when he does that it's good to have someone who 1) catches the ball easily and naturally, 2) turns and accelerates up the field quickly and 3) makes tacklers miss. Cook is the only one who may be that but he's not that now, they clearly aren't comfortable with him playing a lot of snaps. If it's a bad draft pick I wouldn't let that stop me from winning the championship, that's the goal, not proving your draft acumen.
McCaffrey does upgrade this team. If you can't run the ball you damn sure better be efficient in the underneath passing game and get YAC, and yes that is going to inevitably include the running backs. Throwing as much as we have to Devin Singletary and Zach Moss this year is just not efficient.