Send your boss a link to "Negative 2000 Lines of Code"[1] and ask him if he thinks Bill was a shitty coder.
When I was scrum master for two teams I, too, tracked some metrics (for feedback and improvement, not for pay or career (ab)use).
While I did track the number of story points delivered and user stories closed per sprint, one of the things I was more interested in was how accurately the teams managed to hit their estimates (regardless of what they were). In that perspective, delivering too much too quickly was just as undesired as the opposite. We used this to refine the way that we did estimates, story refinement, and sprint planning.
Naturally these were team-based metrics, because software development is a team activity.
[1] https://www.folklore.org/StoryView.py?story=Negative_2000_Li...