The one starter thing is meaningless. There is only one starter at kicker and punter and fullback and tight end. Doesn't make those positions more or less valuable. Plus many teams give significant carries to multiple running backs.
As for establishing a running game, you are still living in the 90s. The league has changed. The Patriots have built a dynasty around using their cap and draft resources at other positions. In the Belichick era they used two first round picks on running backs, picks 18 and 21, who combined for 39 AV.
Teams are passing more and rushing less
And there is a clear correlation between passing and winning that doesn't exist for rushing.
Due to draft guarantees, running backs drafted in the first round get outsized contracts compared their position peers and that is unique among nfl positions.
http://www.espn.com/nfl/story/_/id/...ng-back-round-1-better-awesome-2017-nfl-draft
From that same article, here is the difference between round 1 and round 2 running backs.
1. Running is less important than ever to winning
2. Running backs drafted in the first round get disproportionate contracts compared to their peers in later rounds.
3. The top performing running backs are usually not picked in the first round.
So if you dont need them as much anymore, you cant identify on draft day which ones will perform best and there is an added cost for drafting them in the first round, it doesn't make sense to do it.