The suggestion that managers should have >10 direct reports doesn't convince me. Maybe 30-person reporting groups can work in places where everything else is precisely right, but in most environments this will be a recipe for a power vacuum where people are incentivised to start acting as de facto managers. And I'd sooner have one manager (who, ideally, I had some choice in via picking a job or assignment) than several pulling in different directions.
Most of the rest is spot on, though.