As VPEng, I didn’t use metrics to assess individuals. Too prone to metric gaming.
Instead, I had a career ladder with a detailed rubric describing the skills an engineer at each level was expected to have. (Including communication and peer-leadership skills.)
Managers performed qualitative assessment of employees, using the career ladder as a guide. They relied on tech leads and Staff engineers to help them understand people’s skills, and provided 1:1 feedback and coaching.
We did use impact-based metrics to assess the results of important initiatives. We solved the attribution and lagging indicator problems by estimating impact rather than measuring it, and using a series of proxy measurements (activation, usage, retention, etc.) as a feedback mechanism for revising those estimates.