There are few more frequent visitors to the executive suites of America’s biggest companies than the strategy whisperers at McKinsey, BCG and Bain. It helps that the corner office is often occupied by one of their alumni. Among the chief executives of America’s 500 most valuable companies, 36 spent time at one of the three elite consultancies, according to Altrata, a data provider, up from 25 in 2018. Household names from Alphabet and Coca-Cola to Citigroup and Visa are run by former consultants. But are they any good at the top job?