Then I suggest watching the film again... Minn game.. 8 rushes for 16 yds? He could do better then that not trying if healthy!! His foot wasn't stopping him from throwing mostly ok!
For perspective: TA had 12 rushes for 13 yards against Michigan, and I think he's healthy.
I think this was a really simple situation. TM had a chronic injury and kept trying to play through it rather than get surgery. This happens to probably multiple guys on every team every year. Hats off to him for trying to play through it and hats off to the coaches for giving him a shot (and as thill clearly explained, there was never a chance for a medical redshirt because TM's redshirt year wasn't due to injury).