If we are talking in terms of QB, the data suggests that the back up is guaranteed to start a few games. Casey is also a 1 year addition because if he has the year he wants, he is bolting for the pros. Chubba has better tools and build than Logan but experience trumps all. And he has more of it with this collection of guys and he brings a speed component that gives defenses fits.
Grant and Yant are not guarantees for anything but being in the rotation. Nebraska needs RBs who can flex and catch the ball. Against our two best opponents, Rahmir was one of the best players on the field. Had he not gotten injured, his numbers would have been better, and it is possible that Nebraska even wins an extra game or two based on his output (debatable I am sure). Regardless of that, he has room to improve and transitioning to a new offense, you need experience. He is that and then some for this team. He isn't traditional like an Allen or Ervin, but he is proven unlike those two. I imagine you will see 5-6 catches for Rahmir a game, and with his speed, he is going to house a ton.
I see what you're saying and obviously we are at a numbers crunch. However, those are two guys we are going to have to rely heavily on whether behind the scenes or on the field.