How about: People with similar performance should have similar salaries. I've seen qualified and capable people add no value, and less qualified people hustle to perform well.
Results are hard to quantify. You can jump on a successful project and skew your contribution factor. But what if you are working on important tooling that requires difficult problem solving. This important tooling might not be quantifiable directly like, say, an advertisement framework. It may, however, be more valuable in the long term.