Admin bloat is a far larger problem, and so are the pharmaceutical companies which get to charge the government whatever they want to develop new drugs that often are only marginally effective.
But this "semi-monopolistic trade union" not only inflates their wages (which maybe that's a good thing), but it also harms the lives of the population they purport to serve. Many (most imo) people in the US simply cannot afford the monopoly's prices, and the monopoly has little incentive to innovate. This cartel of doctors actively prevents lower-cost, more efficient alternatives from coming to market.
https://www.noahpinion.blog/p/insurance-companies-arent-the-...
https://www.noahpinion.blog/p/service-costs-arent-exploding-...
However, at the core, US insurance system is the problem because it gets compounded by government trying to regulate such a system, so people do not die needlessly, but not destroy these profit seeking enterprises. So, what you end up with is a massive mess that leaves everybody cranky.