"Health care should be strictly preventative and diagnostic" runs into the problem that not everyone agrees what that means. For a while most Europeans thought that leeching yourself was preventative medicine, or Japanese people thought removing the outer layer of your skin by rubbing it hard with towels was, etc. Nowadays some people have forgotten that vaccines work and don't want to pay for other people to get them.

Health care in the US is definitely stupid and bad and can easily be made better than it is, but all the easy sounding obvious right answers that would fix everything about some aspect of life usually don't pan out in practice.