As you noticed, my previous comment was mainly related to external scrutiny. If we genuinely consider the added value of a CEO to the company and the owner, it’s a slightly different matter. The success of management must, of course, be analyzed by some metric, but what would be suitable? Are short-term goals, which can conflict with long-term goals, being set and monitored? There’s a significant problem with what the owner’s goal is: to develop the company long-term or to maximize short-term profit. Of course, these aren’t in clear conflict, but they can significantly affect the assessment of success.
The crucial factor is actually how the company has developed in relation to its competitors or what its future outlook is. Has the company invested in the right things? However, these are really difficult to put into numerical form as a whole, because there are so many variables to evaluate. It’s particularly difficult to numerically assess the CEO’s success on top of these. Ultimately, it comes down to whether the owners are satisfied.
It’s somewhat the same problem in choosing a partner. Candidates can be evaluated by certain criteria, but because there are so many variables in human behavior, you can’t find a solution through rational reasoning alone; you also have to use emotion. It’s the same in investing and in CEO decision-making. In some matters, you can utilize more numerical information, but you can’t make decisions solely based on them.
This reminded me of a story where Torbjörn Magnusson talked about how he forms a good team with Nalle and Karin and how they get along well. And this was largely why Magnusson was chosen. There might have been a more competent expert found elsewhere with certain selection criteria, but would that have been better for the overall picture 
In the long run, for a company’s success, the emotional side and intuition of a leader are emphasized and decisively influence the foundation created for the future. This cannot be modeled in any way; it again comes down to whether there is a feeling that the right choices have been made.
Each owner also has their own personal criteria for evaluating this success. Therefore, no absolute truth can be obtained about success, and naturally, no absolute number can be defined to tell how well leaders have succeeded. This is why compensation is largely determined by the feeling of how good a leader is perceived to be. It should also be added that due to rigidities in the labor market, including the labor market for leaders, there are many exceptions.