Technically, Fulmer did have head coaching experience before he was "hired" as head coach at Tennessee. He was promoted to interim HC when Majors fell ill in the middle of the 1992 season (as he was the senior assistant coach), and then was "hired" as HC during the next offseason, with a 4-0 "head coaching" record under his belt. Some questionable ethical moves made by Fulmer, as Laphroaig pointed out, but it is what it is. He served the role of head coach when the program had no other choice, giving him head coaching experience, but without the title or permanence of head coach.
You do point out a few examples, though, so point taken, although I seriously doubt that any quality SEC program would hire Muschamp as HC at this point in time until after he gets some HC experience somewhere. I would say there's a very, very slim chance that if Papa Bowden retires/dies, and Richt bolts for FSU, Muschamp could be considered, as a UGA alum. Again, I doubt it, but possible. I've been wrong on several occasions, so I could be wrong about this, too.