I liked what Johnson at I-back in 2021, as he brought some versatility and had decent success back there. However, the coaching staff has a job to keep bringing in talent and let the best players play. Grant and Allen look as the 2 best I-backs by far, and the simple story is that they have beaten out Johnson, Ervin, and Yant (although I was never high on Yant). I think Rahmir can find a role on the field as a combo RB/WR, and that may come in future games as Whipple shows new plays/wrinkles to the offense.
Ameer Abullah was the lowest recruited I-back of his class, but when he got to NU, he showed he was the best of the three. That's all you can ask as a player. Get on campus, and show what kind of player you are, and take advantage of those opportunities.