Chaka
Footballguy
Your memory may not be the best then. Jones (6), Dillon (23), Chubb (2), Hunt (13), Jamaal Williams (5), Swift (7), Denver is pathetic but Javonte (19), Gordon (31) and last year they finished 16/20.I suppose if you're in a sixteen-team league, you can start both. I haven't seen a true RBBC be able to be supported unless it's Chubb/Hunt, and that's actually the only example I can think of in recent memory where you weren't taking a chance at about six points or under if you started one guy and not the other.
You run the risk of 6 point games with any back. You minimize that risk high end RBs but, outside the top 5-10 options (and we never know who those guys are going to be judging by the amount of first round magic football busts). At that point duo backfields are highly viable. There aren't many good duo backfields but there are some and they're worth taking a shot on.
To the topic at hand it is difficult to see Monty & Khalil being a viable fantasy duo considering how limited that offense has been as a whole.