You're just rewording what I am saying. I guess I am not being clear.
Here is one hypothetical based on recent NFL precedent:
If the Lions are good on offense again this year, everyone will want to hire their OC to fix their crappy offense. That guy is going to hold out until he gets the HC slot he wants - like Daboll did.
Now teams are going be like "Ok...who else on that staff can we get?". And they are going to want to get the QB coach (interestingly enough that is Mark Brunell!) or Passing Game coordinator. One of those guys is going to almost certainly get elevated by the Lions to replace the outgoing OC. So...now an NFL team is left with the #3 guy in the offensive organization. How good is that guy really? Maybe super-duper excellent. Maybe just awful. But you are going to be hiring someone who never called plays before. That is a risk.
The college ranks is where you can get a direct OC to OC transition, with the jump to the NFL being the "promotion". But many of the best college OC's just hold out to be come college head coaches.
The bottom line is that the Steelers next OC is most likely to be from one of three groups:
- Rehabbing NFL Coaches: This is where they got Arians and Haley. Something has recently happened to take the shine of this type of coach and they need to go somewhere and rehab their reputation. It can work out. Or you can get Joe Lombardi or Brian Shcottenheimer.
- Unknown Offensive Staffer from NFL Team: This is along the lines of what I speculated on above. Now with like 3 dozen Mkvay assistants it has worked out across the league. Other times, it just doesn't go all that well.
- Unheralded College Guy: This is what they tried to do with Canada. They could go back to that well and hope they do better next time.
All I am saying is that the Steelers have a poor track record with OCs. And the likely scenarios are not without significant risk. The candidate they get is going to have a "flaw" because the guys without flaws are going to HC jobs. The question is how damning the flaw will be...