The biggest problem is that people to this day don't understand the difference between a board/manager structure, and a DoF/head coach structure. And it's funny to read people wanting to apportion blame to the head of football development at United, which is a role that oversees the development beneath the first team. And the same roles do exist at other clubs. Spurs, Arsenal etc (to just name two clubs) have also had people as the head of development beneath the first team. And their remit is to oversee the development of their departments. So for example at Spurs, John McDermott was the head of development beneath the first team, and Pochettino controlled and directed the football side at first team level. Currently at United we have Justin Cochrane who is the head of player and coaching development and we shouldn't blame him for the mistakes at first team level.
The head line below is pretty self explanatory as far as the role of a DoF is concerned.
And as far as contacts go, Matt Judge was the director of contract negotiations in a board/manager structure with the manager having the luxury of having his own personal scouts. Players like Varane, Sancho, Ronaldo were signed under the same structure (I also had no issues with those signings). Because Solskjaer (the manager) didn't report to John Murtough but rather he was reporting straight to Ed Woodward according to David Ornstein/Laurie Whitwell. So there was no DoF structure at that time and one shouldn't be confused by someone being given a title when the manager model was still in existence. But those changes IMO were driven by Richard Arnold, who was preparing to take the reigns as the CEO, and wanted to be guided on the football side of the club by having the buffer of a DoF between himself and the head coach, which is a sensible move imo.
The role of the DoF is a simple role and should be evaluated over several years. And the experience one needs to be a DoF is to be able to run multiple football departments on the football side of the the club according to Dan Ashworth. And one shouldn't compare the way the RedBull clubs operate as something we should also do because we're Manchester United and not a stepping stone club that buys young players to then sell for profit a few years later.