One measure of a high-quality C-level performer is the quality of their teams. The best C-level people can bring in very high-quality managers and individual contributors underneath them. Below average C-level people really struggle on this front.
Also, for some C-level roles there are good and objective ways to measure performance. For example, for a Chief Revenue Officer you have (obviously) revenue. There are a ton of confounding variables of course but in general CROs who consistently out-perform plan are better than those who consistently under-perform plan.
Also, for some C-level roles there are good and objective ways to measure performance. For example, for a Chief Revenue Officer you have (obviously) revenue. There are a ton of confounding variables of course but in general CROs who consistently out-perform plan are better than those who consistently under-perform plan.