Let's face it. As long as Brady is running this offensive unit, they are never going to be a team that relies on the run first to set up the passing game type of team. It is just not going to happen.
They have fared very well, better than most teams could, with have a running game that is passable, not great. They actually run for as many yards, combined by all of the running backs, as some teams do using one running back as the main carrier of the football.
This team, as far as I am concerned is fine at the running back position. If they choose to add a veteran RB, so be it... but far too much emphasis is being paid on them getting better at the running game.
IMO, once they decide to use the running game more often, that will be the time that the offense begins to stumble.
Going away from what your strength is, in this case the passing game, can only be a pathway for defeat.