I don't think it's that simple. United have hired proven managers. Every manager we've had has underachieved.
There's a lot wrong with the way the football side of the club is run. We've been blaming the managers, but we should also understand that they do not work in a vacuum they need a good squad, a supportive board and a competent recruitment department.
This is not a defense of Ole by the way, because I don't think with the shambles our club has been since SAF can be used to fairly assess a manager. I'm just pointing out that the board that has overseen the past (failed) managerial appointments, and given us this squad of not yet good enough youngsters and past it deadwood will probably oversee another failure no matter who the manager is. We'll just appoint, underachieve, sack, rinse, repeat.