From Peopleware: “In the 1985 Jeffery-Lawrence study [from the University of New South Wales]…they investigated the productivity of 24 projects for which no estimates were prepared at all. These projects far outperformed all the others…Projects on which the boss applied no schedule pressure whatsoever (‘Just wake me up when you’re done.’) had the highest productivity of all.” I read 20+ books on management and leader…
While I too despise Scrum, the causation could be runming the other way: the Bosses that have a better team could be more likely to let them run without major pressure.
So it would have to be both: the devs are good and don't need hand-holding, and the manager is able to deal with the lack of transparency that "it'll be done when it's done" comes with.