Obviously assistants and associate HC’s can get head coaching jobs, but I don’t think there’s any advantage to that if you’re already a HC, unless you are hoping to get the HC job at the school you’re going to, hence the Robie comment as I mentioned.
All the guys on your list had never been head coaches before. And half of them were promoted at their own school.
Similar to the Coleman Scott discussion, the COL difference is likely a factor. But I don’t think the move helps him get a different HC job unless there is a succession plan with Robie.
Oh and Columbia is not below average. They finished above average this year including ahead of half of the coaches you listed.