Disagree Dave, in these days, a dof is needed more than ever, problem us we didn't hire one, and we never gave him the true power of one either.
A proper, good dof, we avoid the manager to yo mess, we avoid the subsequent recruitment mess also.
Simply put, we had a dof say at the time of Martinez leaving, we 100% don't go for a polar opposite manager when he leaves, we would have targeted an attack minded manager, thus transition for existing players is easier, recruitment becomes consistent etc.
Look at Chelsea for example, 6-7 managers in ten years or so, but all through they have had a "style" which those managers have fitted into, meaning a manager change doesn't require selling established players because they can't fit the new style etc.
As example - Martinez here for three years, his successor should have been a someone who had at least an attacking mentality and who valued technical ability etc