At least 99 companies in the Standard & Poor's 500 Index paid their CEOs at or below what Crystal calls their "going rate" last year, according to his study, which tracked 177 firms in the index. Moynihan, 54, was paid $13.1 million in 2013, 30 percent below what Crystal calculated as his going rate.

Chief executives typically receive boosted pay when their company's performance improves, Crystal said. When performance stalls, compensation doesn't always follow suit. Some U.S. companies have been able to tie pay to performance better than others — and improvement at those firms is happening at a "glacial pace," Crystal said.

"If you go down the aisle at the executive-pay supermarket, the quality relationship to price is not as robust as in a regular supermarket," Crystal, 79, said in a phone interview from his home in Las Vegas. "You can pick up someone of very good performance for less than someone with very poor performance."