It all looked perfect on paper. Between 2013 and 2015, 3G--the Brazilian private equity firm credited with "reinventing the consumer industry" by applying its deceptively simple "cost-cutting and deal-making" approach to Burger King and AB InBev--teamed up with Warren Buffett's Berkshire Hathaway to acquire and unite packaged-goods giants Kraft and Heinz. The move brought classic...