If we have a plan, we have a coherent and stable system, a manager who knows what he is doing, most of the players we sign or already have will develop, even some of the ones perceived as lower qualty. If we have neither of those, they will fail. It's systemic. The elements which work without the system being good are called exceptions.
The failure of this club at the moment is managerial. Which means, board + manager. The manager the most since he is the one that manages the team, but the board become guilty by association by vouching for the manager while at the same time going after players the manager doesn't want or doesn't value. These things must be in sync. Get the right manager so you don't end up signing Barca-profile players like Arthur and De Jong who are, hilariously, not the right profile for the manager you have.