It can't be assessed by a single dimension, but it doesn't have to be. A high quality engineer absolutely can rank the technical competence of other engineers in his field (not just computer science) with a high degree of certainty, and that's all you need. The "it's complex" argument is similar to the "it's a tradeoff" argument in that both are easily abused to justify any bad decision.

Technical competence is frequently Mismeasured in a single dimensional, objective contest.