Quinn is a lefty and he's one of three offensive defenders who might be available to Detroit this draft. Dobson is a righty, and the only two-way finesse defender of the four defenders who could be available to the Red Wings. So, despite Hughes' skating, Dobson seems less ordinary. Plus, considering Dobson is ten months younger and therefore less seasoned than Hughes, I think you have to expect Dobson's got more upside, both offensive and defensive.
Dobson can close the gap on Hughes and Bouchard with development. Simultaneously, with Bouchard, you can't expect his offense to translate seamlessly into the NHL. Bouchard has gotten points from all over the place because his skating is a real advantage for him in juniors, but his skating wont stand out so much in the NHL.
Not to bag on popular rankings; they serve a purpose. However, major published rankings often conflict a little with one another, even while all them are off on nearly every player in every draft.