I think a lot of people are waiting to see if this is the magic addition that we need this year, including me.
Here's my take, in response to your assumptions:
If all this was about was that he was behind the last two starters, wouldn't he have certainly stayed for another year? Can't we guess that he might be buried much further than that on the depth chart, and had no prospect of playing next year? So, assuming that there were no other issues, one has to be at least a little concerned about what might be left of his talent since he's played very, very little football over the last 4 years?
Regardless, if this guy was a legitimate 4-Star recruit out of high school, we certainly owe it to ourselves to give him enough carries to see if he has it.