The problem isn't that they deny claims, the problem is that they exist in the first place. The industry has evolved from a nice-to-have to a downright necessity, because its existence has changed the entire concept of market economics.

The existence of an industry of competitive, for-profit middle-men means that scrutiny must be applied to all charges to increase margins. This ends up spiraling the cost of care up to the point where it's unobtainable without it, necessitating its existence.

Tying it to employment also means that changing jobs can be a significant risk to the health and wellbeing of your entire family. Even worse, your employer cutting costs by changing providers could do the very same at any point.

The combination of "money is speech" with this means that their profits must also be "invested" in protecting potential profits, by means of government lobbying.

This is why for-profit health insurance industries are unsustainable. The only solution is a non-profit entity in the marketplace that has such a large risk pool that the level of scrutiny isn't necessary because they have the negotiating power to drive costs down to acceptable levels. This is government single-payer or Medicare-for-All. There is nothing saying it can't compete with private insurance, but private insurance should not be necessary for life.