Roche's latest breakthrough could be a game changer, but it's still too early to say.When a major player announces good news in a lucrative market like weight loss drugs, it's often enough to drive shares of competitors down based on the assumption that they will have struggles ahead.That's just what happened after an announcement by Roche Holding (RHHBY 3.03%) on July 16. Shares of Novo Nordisk (NVO -0.88%), Eli Lilly (LLY -2.02%), Structure Therapeutics, Altimmune, and Viking Therapeutics all took a hit. ...