Really don't see the problem with them so long as the definition is clear.
It's how the system works in other countries in Europe where they don't appear to have as many issues as we appear to have with the system.
The problem is, that the definition of a manager in this country in the eyes of the press and the fans, is somewhat antiquated it's a Brian Clough style of management where the manager is the absolute boss of absolutely everything. It's something that is increasingly becoming marginalised in modern football.
On the buying of players issues specifically - i don't really see the problem, so long as it's done in the right way. In that, they work with the manager to decide what kind of style of player is required, then the manager leaves it to the DoF to find the kind of player they want and trust them to deliver the goods.