I think the answer depends on the nature of work and the level of the direct reports. It’s harder to manage a large group of folks who are all learning the job/organization than to manage the same size group of folks who are familiar with the processes and policies of the organization. You can use team leads to help with training, quality control, and workload distribution but the manager needs to be able to spot problem areas within the group and provide developmental opportunities (training courses, assignments, etc) to improve/enhance performance. I once had 50 direct reports when I was in Industry and it was almost impossible to give meaningful performance reviews with that many people. And as an employee, I want my supervisor to be able to fairly assess my work, my strengths and my weaknesses.