Other legitimate options? They were FBs. They don't get the ball a ton, period. I'm not really sure where you're even going with this or what argument it is.

The point was that nobody was there to really take many carries away from Unga... (And no, you can't count FBs, and for that reason I won't even consider Lasike, who they sort of list as a combo but we know he's just a FB). FBs aren't primary ball carriers.
When Hill runs that much (yes I understand some are the result of failed pass plays) it's not comparable at all to who Unga played with. He's basically a RB out there with that number of carries he finished with.

Also not sure what where you're going with the whole PT thing. What does that have to do with anything? Is that like saying Jamaal "wasn't good enough to start" but Unga was? If someone is forgetting something, it is that Unga was a RS freshman. Jamaal was a barely 17 yr old true freshman. Unga got 4 carries his "freshman year" and then took a RS. Williams became the starter after a few games.... And we all know it would have been a bad mistake if they kept Alisa (if never broke an arm) over Williams.