Costs for treatments are standardized and agreed on nationally: you can go and look them up. Your bill has codes on it that match this list. It is called TARMED: https://www.bag.admin.ch/bag/fr/home/versicherungen/krankenv...
Insurers under the LAMal system are restricted in what they charge for premiums too, and must negotiate this with the confederation.
There's still a lot of scope for private companies to make money here. LAMal covers what are deemed essential treatments, which is most things you need a doctor for. If you want 'alternative' medicine there are insurers you can pay more money to for that. Likewise, if when you go to hospital you want a guaranteed private room every time, then you can pay extra for that. And so on.
Even on the basic system, you have a choice between telephone doctor for all appointments except emergencies, family doctor for the same or the unrestricted system where you can ring up a specialist yourself without referral. Needless to say, the one where you ring the insurer first is cheaper, followed by the family doctor (similar to the UK: referrals are controlled via your GP).
I don't see any poor doctors here, or poor insurers either (insurance, behind banking, is a massive business here). So it is entirely possible to design a system that includes a large amount of private insurance that also doesn't randomly try to bankrupt people for getting stitches.