Competitive Bidding and Lower Costs?

Kevin Drum says, "There's good evidence that competitive bidding is a useful part of the healthcare discussion and can indeed help control medical costs. But how much?" There are two studies I have seen on this, but that I do not understand and they both say that competitive bidding could reduce costs by about 8%.  However, two real-world caveats:
1. Medicare Advantage was supposed to do this and it has ended up costing taxpayers more than regular Medicare.  That is a pretty big strike against competitive bidding.  In theory it could work, but the only example of it in practice is a complete failure. 
2. One of the reasons that competition works poorly with Seniors is that a significant fraction of Seniors have some form of dementia or low literacy or depression, or some other difficulty shopping for something as complex as health insurance which is hard enough for an Economics PhD to sort out. 
3. Outsourced to Kevin:

...just focus on private insurance. When a corporation provides health insurance for its employees, what does it do? Answer: it sets some minimum requirements and then solicits competitive bids from insurance companies. After it gets the bids, it chooses one of the low bidders. This is competitive bidding in its purest form.

So how has that done at holding down healthcare costs? In case you need a hint, the charts on the right tell the story. Since 1999, according to the Kaiser Family Foundation, group insurance premiums have gone up 168%. And CBPP reportsthat private insurance costs have risen faster than Medicare costs consistently over the past four decades.

Private corporations all rely on competitive bidding, and it just hasn't done much to hold down costs. That's because the real source of America's high medical costs is the fact that we simply pay more than other countries for everything we get: more for doctors, more for procedures, more for hospital stays, more for drugs, and — yes — more for insurance.

The mechanism for competitive bidding is a voucher program or "premium support".  The major way that Paul Ryan's plan cuts the government's costs is by just capping government expenditures and letting more of the burden of paying increasing health costs fall upon senior citizens as health costs rise.  Ironically, this plan would eventually turn Medicare into something similar to Obamacare, but Ryan opposes Obamacare.