Managers from the outside tend to hire somebody from within that can give them an idea of the club, its culture, whom to talk to and how things are run. Usually clubs had people in place for that. Inter used to have Giuseppe Baresi who had covered every coaching role possible from scout right to U23 coach and assistant manager. United seem not to have that mainly because our coaching staff is crap + our former players tend to resign the moment they are not given a top spot.
In my opinion ETH had chosen the perfect man. Mclaren has managerial and assistant managerial experience, he knows United and the EPL inside out + he also know ETH system well. He's also a person from the outside as well which means that if United win a trophy the manager won't be asked if his assistant is ready to step up and take his place because, you know, mates and DNA. In my opinion ETH had been flawless till now. He came in early, he set everything in place and he promised change without throwing the current squad under the bus (which would have turned these pile of hot garbage against him from day 1). I like the guy