I don't expect someone who hasn't played meaningful football, coming off two big injuries to do squat. That's just not reality, he won't be in Football shape at all.
The biggest issues with your comparison is Allen and Kelly =GREAT. Do we have TWO HOF WR on the team? (Reed and Lofton) nope. HOF RB, Nope. No huddle, wide open Offense? Nope. And Marv was a better game manager than McDermott.