"Like the Obamacare exchanges, health plans in private exchanges don't add to their bottom line by becoming good at cancer care, diabetic care or at any other expensive-to-treat disease.... So what can be done? ... [H]ave all the health plans be offered by a single insurer, say, Blue Cross.... [M]anaged competition only works when health plans are prevented from doing what is in their self-interest to do.... [E]mployer risk adjustment.... [H]ave the risk adjustment be administered by the health plans themselves."