We have Philbin and Sherman. They have Ryan and Sparano.
And what do we know about Philbin's ability to be a head coach? Ans: Absolutely jack shit. We know he was a decent OC in Greenbay. But every single HC was a decent OC or DC before becoming a HC. Some make the transition, many don't. There is absolutely no reason to think at this point Philbin is more inclined to follow the foot steps of Shula instead of Cam Cameron, who also was a decent OC.
As for Sherman, he was fired from his last two jobs. That is never a good sign.
Ryan was more than a decent DC, he is one of the most brilliant defensive minds in the game. Like with many he has not done a great job in transitioning from DC to HC. If I owned a team and could steal whoever I wanted, I would have Belichick as my HC and Ryan as my DC.
As for Sparano. Not a good HC. But he was a good OC. He is an OC again.
I really can't see how you can claim Dolphin's have an edge on coaching.