KPI's and their attendant performance reviews and rating systems are the bane of corporate existence and add almost no value.
We (corporate leaders) should indeed measure contribution but also engagement, innovation, adaptability and growth. Because these are "gray" or "squishy" areas, they're uncomfortable for many managers to use as metrics of performance assessment.
Asking leaders who work in a metrics-based environment how they "feel" about someone's intangible skills and abilities is tough and can be uncomfortable. It's also a potentially dangerous area to wade into when it comes to equality of pay, promotions and ratings.
Because such a low percentage of leaders are able to effectively evaluate talent, performance metrics serve as a guidepost. The smartest and most innovative leaders and companies can and should see beyond performance and use less easily measurable but more effective indicators of success.