> 5% of denied in-network claims were turned down because the care was deemed not medically necessary".

I think the truth is murkier than what you're providing. With the caveat that I am presenting a strong case here that likely isn't what occurs most of the time, consider this:

A person may require long-term therapy after an illness. There are data suggesting that beginning this therapy works better once you attain a certain level of clinical recovery in the hospital. There are also data suggesting that it's better to begin the long-term therapy as early as possible.

Both sets of data are, on their face, credible. There is no obvious reason to always believe one set of data over another. Reasonable people can make reasonable arguments to reasonable listeners for either case. Note that this does not mean that there is not a 'correct' interpretation for any given person's clinical situation!

So what does your insurance company favor? Obviously it will always favor the less expensive option, and there will be no way for them to be convinced otherwise because the underlying question is just not well-determined.

But in a case where either treatment choice could be reasonable, doesn't it seem like a better answer for the insurance company to defer to your doctor rather than their own assessment? Whoever is making that determination at the insurance company doesn't know you, hasn't treated you, may or may not have more expertise on the specific illness than your doctor, and as you pointed out the insurance company doctor is ultimately motivated by keeping costs low more than they are motivated by keeping you healthy.

Obviously I can see why the insurance company would prefer to be making decisions about your treatment, but it's not obvious why any of the rest of us should view that as an optimal or even acceptable way of running healthcare. It's essentially the car insurance model but with vastly higher consequences, and it's not great even when it comes to car insurance.