I see your point, but I see an implicit either-or choice in it. I must ask: would it not better for team cohesion and efficacy if managers were doing 30% engineering, and engineer had the option to have their word in management? I have experienced that, and although it was maybe more tiring for the manager on the short term, he was a real part of the team, and decisions were never taken in contradiction with technical factors. Vice versa, engineering was more targeted towards real customers needs that if we had no manager. On the long term, it was less work per product, because the more integrated team ran more efficiently.