That was one of my first lessons in the antepenultima year of master's degree:
- We were teams of 6 people (across 130 students),
- Every team in the class was free to choose to have a PM or to have everyone equal,
- We'd go through ~40 projects in one year,
- We were all the same kind of students, same background, no individual ability at the beginning.
We all started with self-organized groups. 50% of us failed our first projects and others got angry, mostly because one person didn't respect the deadline or because of the discordant directions we took (Our divergent was > 0).
Third or fourth project, we all decided to choose a PM, a quality person who'd provide the document templates, and 4 active workers. The PM had all credit to choose an option when several directions were available, and at the end of the year, the PM could decide how to assign the marks. We all performed properly at the 3rd project, met 95% of our delivery dates, and got on well much better together.
Most groups reused the same pattern on the 36 other projects of the year, albeit we switched roles between the workers, quality person and PM.
We did the experiment, and the answer was: Yes, everyone created equal, we needed a PM.