Some years ago I started doing graphs of code contributions across the year (yeah, wrong thing to measure, I know). A funny thing is that people considered "high performers" could be made the worse performers depending on how you cut the data. Basically, performance had a wave behavior, and nobody was at 100% all the time.

That is a good argument for diverse hiring: people will have bad days/seasons, fact of life. If the team is diverse is less probable that those bad days will correlate between different employees.

I did that once and one contributor had a huge negative value. His team had reimplemented a feature and his major contribution was deleting the old version.