How has the trend of vertical integration among major health-care intermediaries, such as insurers, pharmacies, and pharmacy-benefit managers, impacted the overall profitability and dynamics of the U.S. health-care system? In the context of the current challenges and criticisms facing health-care intermediaries, what potential disruptions and competitive forces are emerging, and how might they reshape the industry's landscape and profitability, with a particular focus on the role of newcomers like Amazon and innovative approaches by upstart health insurers