1. There's an efficient market, and CEO pay reflects the extra value they create. In other words, a $100 million CEO is worth $50 million more than a $50 million CEO, so your economic outcome is the same regardless of which one you hire--except that larger companies will extract more value out of a given level of managerial talent, since they can amortize it over more underlings/revenue/whatever.
or
2. CEO pay and company performance are totally random. But for that to be the case, you'd have to deny that there's any such thing as being able to identify and pay for a talented CEO. Maybe! But every time I've interacted with large company CEOs, I've noticed that they tend to be very bright, and they work extremely hard. People who are in the 10th percentile of public company CEOs--the kinds of people who bankrupt companies--still seem to be in about the 90th percentile of smarts and energy.
I don't know of another theory that could explain the data as presented. Either the process is random, or it selects for people with certain valuable skills. If the system tends to promote skilled people, you'd expect the companies they run to have a higher return. Unless, of course, they capture that value for themselves.