That's the argument presented by Ed Meese in his brief with the Supreme Court. But it looks like justice Thomas doesn't agree. If you look at his concurring opinion, on the first page he writes:
But, I am not sure that any office for the Special Counsel has been “established by Law,” as the Constitution requires.
I don’t see there that they differ. Thomas is saying that there is no apparent basis to derive prosecutorial powers for Smith, being that he doesn’t hold a legally established position, on top of not having been confirmed to a position with its own prosecutorial authority. At this time, Special Counsel is a extra-legal label rather than a position.