I must say that i am totally against this trend when coaches get a chance to coach big club just based on the fact that they are legends of that club. I don't see any logic in that. Based on what? What owners think at that moment? He was great player so he will be surely great manager?
You must earn biggest jobs in the world. Being a player or manager of giant clubs is the most difficult job (and achievement) in football. So you must have people who know what they are doing. Being a CEO of multi billion company is not a place where you "learn" how to do your job.
People use Zidane and Pep examples always. But they already inherited top squads in 2 club league. And yes, time showed that they are good coaches. But again it was a gamble which could have gone in opposite way. Like Real did with Solari for example.
Anyway, coaches should prove themselves before getting top job.