Barry Sanders split carries, he almost always was benched on any & Goal situations. I'd say he was pretty good.
I think you have to take into account the game at the time. Before, if a running back had 8 1000 yard seasons, they were guaranteed the HoF. But now, 1000 yards isn't what it used to be. Same goes with QB stats with nearly all of the top 5 surpassing 4,000 yards, when it used to be rare. If the style of game is that you split carries with another back (although you still get 25 a game, we'll say), you shouldn't really be punished.
I think Warner is talking more along the lines of Ahmad Bradshaw and Brandon Jacobs as backs who get roughly 50% of the carries for the season.