All these guys (including McD) have been beaten positionally and possess less recovery skills than Miller has already.
As far as when the context for Miller can go away - gradually over the next three years.
Every defenseman has been beaten. Orr and Lidstrom got beaten on occasion, but Girardi, Staal, and McDonagh were all far better at positioning than Miller last season.
Again, Miller's future is unknown, but his positioning last season was poor.