OU's recruitment of running backs starting with the 2015 class (Riley's first year) was likely impacted by the presence of Perine, Mixon, Ross and Brooks already on the roster, so only Anderson came on board. A similar scenario in 2016, when only Adams came.
Now with Perine and Mixon leaving early, only Anderson (recovering from a neck injury and coming off a medical redshirt and missing two years of football) and Abdul Adams are left over.....but 3 highly touted freshmen backs are here and are all said to have a chance to contribute in 2017.
The 2017 class was ranked 7th, the 2016 class was ranked 16th since Riley was hired in January 2015.
Right now there are 5 running backs, 9 WR's, 2 hybrid TE's, 3 ZB/FB, 4 quarterbacks and a slew of offensive linemen on the roster.
Riley is not having problems recruiting good offensive players.....and throwing him under the bus for how the roster has evolved ( through injuries, early exits and suspensions) since 2015 is unfair and irrational.