Investors need to watch MGM's performance versus the S&P 500.Conditions are finally looking up for MGM Resorts International (MGM -1.93%). After years of pandemic lockdowns, its cash-producing casinos in the Chinese special administrative region of Macao are well into a recovery.However, investors with longer memories know the pandemic's effects on the company and other downturns. The question for investors is whether they can earn market-beating returns with MGM Resorts under such conditions.MGM Resorts ex ...