That's fair, but I guess it depends on where you set the bar originally for FWP. If you had him in the 10-15 range, with some concerns that he may lose some goalline carries (like most people had him most preseason) I don't think he moves much from there. If the last preseason game and the Miami game had you really gulping the kool-aid that he's going to be a tier 2, 5-10 running back, then you may want to temper some of the enthusiam.
I don't think that the combo of Dookie/Duce/Haynes is any more of a threat to the number or type of carries than FWP will get than the combo of Duce/Haynes/Cobb was. He was signed for Depth. He'll probably see 100-125 carries this year, none of which FWP would have seen anyway.
ETA: This signing (like many others have said) speaks the loudest to me about what they think about Duce this year. He's old, injury prone, and he sucks. At least with Dookie, he's young, injury prone, and sucks. Slight improvement.