I used to work for a company that managed HMOs. The business model failed because while, yes, it did put physicians in charge of the spending, it could not control the population of clients.  One premature baby or one open heart surgery could greatly impact the claim experience and affect the doctors' income.  HMOs faded away because the premiums got too high or the service too restrictive or both for it to be a viable model for a normal patient population.

Kaiser is the only model that seems to work and they  manage by limiting services and hiring young or foreign doctors at lower rates than when independent physician groups pay.

Sadly, as long as it costs a lot to keep chronically sick patients alive, healthcare will be an unequal burden and costs will continue to rise. 

No easy solution. We have to decide what we want to support and what we don't and stick to it.