Yes, of course school managers should be curriculum leaders based on their experiences and expertise to manage both human and material resources adequately in their various schools they managed.
School managers as curriculum leaders- They can be curriculum leaders since they may have had passed through that level of administrative duties, but Heads of departments have also the function to monitor, lead, train, manage teachers in the department.
Delegating duties can help to properly manage the functions under school managers since HODs are to also to these functions of curriculum planning and delivery.