I worked for a major insurance company for a decade. I'm not an expert on all the costs, etc. but I do know a tremendous amount of resources are spent trying to administer the huge number of different plans for each of the hundreds of groups they have. It's a significant cost of insurance.
That company used to go to the regulator and get yearly premium increases of 50%. They were banking a huge percent of "profit" each year.
If you are going to have the gov't mandate that everyone has insurance, then yes, it needs to be in a way that 1) doesn't bankrupt the insure e and the insurer. I can't see that happening without lumping the healthy in with unhealthy, and then limiting how much treatment really happens. But that latter point is a different and very sticky issue.