The second biggest flaw in your agrument is that all of them were in charge for at least 2 seasons except Kampman-who Boyle didn't appoint and Malpas-no explanation needed. So if your asking for him to give the manager 2 years to get things done, he's been doing that all ready.
If you asked Butcher at the time I'm sure he would have thought he was moving onto bigger and better things, plus his time was coming to a natural end anyway, and McGhee thought the same thing in the summer.
Infact the team Butcher took over were Austrailian Champions and had got to final of their version of the Champions League had they not(not sure if they won that), so I'd say that probably is bigger and better things.