So what you are saying is D. O. F are a useless waste of time, I agree
Very few clubs operate without a DoF nowadays.
Football has evolved away from the sole manager model in the same way it moved from having a committee to select teams and decide purchases and promoted the trainer into a manager to assume most of those responsibilities.
Football has become more complex , the scouting system has become global , the academies are expected to be capable of producing players to segue seamlessly into the preferred playing style of the first team , or recoup some of the outlay.
Players have become more powerful than they once were and their welfare must be attended to.
Managers themselves move around more than they used to and a competent and successful DoF provides stability and continuity from one manager to the next.
Consider ManU’s decline since the departure of Ferguson in the absence of a DoF.
Ultimately a DoF allows a manager to concentrate on the role he was primarily hired for, to coach, select and guide the team to success without getting bogged down in the minutiae of administering a multi million pound business.