The same could have been said about Haley before he went to AZ, but Haley went on to run a top 5 O with AZ before becoming a head coach. Sparano was never a full time OC and the Dolphins highest offensive ranking in his 4 years here was 12th. Other teams D would talk about how predictable the O was and how they knew what plays were coming. That doesn't mean much either since he was a head coach and not an OC with the Dolphins, but I think it is just as valid of an argument as those who will argue that he ran a top 5 O in Dal.
You have said the correct response to the hire before, which is I don't know. I don't think anyone does.