I think the myth is that EVERY team should have a "bell cow" RB for them to have success. It all depends on their offense and style of play. I could care less what the rest of fthe league does and how they run their offense. But in Dallas situation, their BEST teams and most successful teams were when we had stud RBs and the running game as the priortiy and the passing game complimenting. it. No coincidence that the success has come when Calvin Hill or Duane Thomas was carrying the pigskin, Tony Dorsett and Emmitt Smith, and then Murray.
The mediocre teams have been when we have a RBBC approach because we had NO runningback that was worthy. Which it seems may be happening this year as well. And of those top 10 offenses listed, 6 of them had backs over 1000 and ironically Denver has had more success with a bell cow than RBBC. NE does not use RBBC, they use one til something goes wrong whether injury or play suffers, and then change to another one. They don't use them to share the load.
But as the poster above stated, when you have Manning, Brees, Brady, Rogers and Luck as your QB, you are probably going to emphasize the pass. Our TEAM success seems to be better when Romo is not having to carry the load. Nothing wrong with that, as great as Elway was, once he had help from a bell cow runningback with a running attack, he won two SBs.