It looks like a case that could be solved by just moving the maxilla forward, but 8mm is a lot. It would change your nose. So he's probably right you don't need double jaw, but double jaw might produce a better result by splitting the difference in the movement of each jaw. Some people get sag under the neck when moving the mandible back, though, and there's probably some apnea risk, too. I'd say get some more consults and ask about these things.
