Agreed. But there are still some things you'd expect to improve on if he were an upper-level HC that didn't. Let's say we could clone a 2005 Payton, before he got to the Saints. If the Saints made Clone-Payton the interim HC instead of Rizzi, would they still have finished with a 3-5 record? I think not.
That should be the standard. If you want pretty good, just get McCarthy.