I have worked with a lot of managers in my time and, with respect to those I have worked with, few of them have been great. I don't mean they were poor managers, I mean great as opposed to "just" good. It takes something special to be a great manager.
Increasing a scrum team’s velocity can become the metric to focus on. A team with a higher velocity will deliver more work, faster. Who wouldn’t want that? Surely, all the team have to do is work harder, right?