Every dollar of profit an insurance company makes is an unnecessary cost. It should be returned to the customers because it means they were over charged. That’s the biggest opportunity for cost savings
A most efficient insurance program would be a closed loop.
Any leftover money not spent on care would be used to reduce premiums the following year and/or be saved for higher claim years.
I wonder how that could exist in the US? Perhaps these health sharing ministries are as close as we'll get: https://www.medishare.com/
However, I don't think the problem is truly fixable without Medicare for all or similar single payer scheme. There is just a huge gap in not just bargaining power but just knowledge of the market information between the seller (hospitals and health care providers) and the buyers (sick people) that a free market solution can't even work in theory. Even if you ignore the fact that I can't exactly shop around when I have an emergency any more than I can shop around when my house is on fire. The only viable solution is single payer and the sooner we get there, the better for everyone.
https://www.nbcnews.com/health/health-care/health-care-cost-...
Commercial insurers are already required to rebate premiums if their medical loss ratio is below the limit.
https://www.cms.gov/marketplace/private-health-insurance/med...