I not a worrier about stats stuff
But did you look at the YPC in the 4th qtr vs Rice when the subs were in and play calling got pretty blah.
We have been spoiled by two stellar backs the last 2 years. That said, while we don't suffer versus all but 3 teams on our schedule with Williams, while being a great 3rd down back, is not the best RB on the team. It will take a bit to find THE guy who can exploit the gaps more explosively than Williams does. It will take some time and experience.