Not saying that teams don't have two roster-worthy RBs, but having both on your team could lead to severe inconsistencies.
When I say RBs are overvalued I mean I see all the time fantasy 'experts' advising you to pick two RB in the first two rounds, or RB-WR-RB. Obviously 10 of the first 12 picks should be RB, or something similar to that. RB is the most important position in football, but it is not as hard a position to fill as the season progresses. Why take a risky player like Dillon (which I did) over a more stable WR? There will be another Jones-drew this year, and if you have the need at the position you are more likely to sniff him out. This year I'm going to try for stability in my players rather than the flashy risk-for-reward guys.