The food giant's breakup may look bold, but some investors aren't convinced it's enough.Kraft Heinz (KHC 0.44%) is back in the spotlight after announcing plans to split into two stand-alone companies. Bulls see it as a long-overdue move to unlock value and sharpen focus. But not everyone's buying the optimism.For a growing group of investors, the Kraft Heinz story looks less like a comeback -- and more like a rerun.Beneath the spinoff headlines, bears point to three persistent issues: weak growth, brand fat ...