It would be an improvement until premiums increased and/or there was a shortage of services, likely in the form of longer wait times. That would be a net benefit for some patients and a net loss for others.

Given that claim denials most often happen after the services are rendered the shortage issue is probably not that significant.

But nonetheless health insurance being affordable only because insurance companies can simply choose to not provide service to their customers and if people stopped forgoing necessary medical care there would be shortages aren't I think the points you think your making.

Claim denial isnt about (mostly) fraud prevention. It is about cost control.

Doctors and patients have no incentive to control cost and select cheaper and inferior treatments.

Cost control? Think about an insurance company for a moment.

They could pay their CEO less.

They could not engage in needless advertising.

They could refrain from paying dividends to shareholders.

The list goes on...

Yes, insurers adds new costs, but they also check other costs.

Every health systems has and needs some mechanism to deny potentially lifesaving treatment.

My point is that even when you abolish private insurance, you still have someone in the hot seat saying who dies because that care is too expensive.