The thing is though, a good manager usually shows he's good within 1 or 2 seasons. Ferguson was an anomaly. If it's year 3 and you don't know if you have the right manager, it's a good sign you don't have the right manager.
I mean, would any of us be concerned about Ole being given more time, as if what United are lacking is merely stability? I'd love for him to be given another 5 years, because it's pretty clear he's not the man to restore their dominance.
I really think that it's whatever a manager "is walking into" which sets the tone for patience and expectation levels etc. Ferguson walked into a United who were underperforming and had been for some time. Back then, a notable improvement curve or an anomalous trophy was all that was needed to buy a manager a patience dividend from their club. However, in modern times, it's been recognized that good managers can usually get a 'tune' out of a poor side more or less instantly, and at the top level, this is what they're expected to do, even whilst they attempt any re-build or strengthening projects. Mid to lower level clubs, or even Championship clubs are now likely the only ones whose trajectory suits the 'unearthing' of a new Ferguson, because there is a steady growth curve for them to navigate, should they be successful.
The manager whose been briefed to maintain ongoing success without having any 'dips' or 'stutters' is an entirely different breed, and this was never going to be Moyes. To a great extent, it wasn't Souness [for us] either, or Roy Evans. Chelsea, for all their shenanigans hiring and firing have probably established the best template in recent times, but this was all accomplished by a very ruthless and single minded executive operating above the managerial position. Manchester United, having not only lost their "Ferguson"....have also not had an "Abramovich" cracking the whip on their succession managers which basically puts them in an operational limbo with no real advantages over any other clubs who just have to keep trying managers on for size, hoping that they'll eventually find a nice "fit."