Harrison and Mitchell are more of WR3 or WR4 players at this point. Their production has been solid for those positions, but not spectacular. Neither are going to wrest the WR1 from Collins or the WR2 from Greathouse at this point.
Yes, I would have much rather had a healthy, 5th year senior Chris Tyree on this squad, since his potential would have been higher, and maybe this could have been the year, but given how his bad luck with that groin injury played out, he has basically been robbed of another opportunity to showcase a full season's worth of talent.
Still, given the QB situation, I'm guessing he wouldn't have had great production with Riley Leonard as the QB, and I doubt Coach Freeman would have moved him back to RB, since it's already quite crowded there in an excellent way.