Every country's healthcare system rations care. Demand is effectively infinite and resources are limited. Socialized systems tend to ration by restricting supply, forcing patients to wait for expensive treatments or simply not offering certain treatments at all. That might be a net improvement over private insurance but there are certainly some downsides.
Perhaps this is a sign that a health insurance company is inherently a poor way to provide health care to a country.
> Their role in the system is to more or less to do rationing / make resource allocation decisions
And they increase their profits by rationing more. And as is so often pointed out to me, the highest priority of a private company is profit.