Lots of Americans, anecdotally, skip out on regular checkups or checking on minor ailments because of anxiety about paying copays. And then eventually something that could've been easily treated when detected initially blows up into an expensive ER visit or requiring specialists.
A good chunk of this could be solved if we stopped using the ER as the catch-all emergency net for literally everything.
This is why hand waving away "bargaining power" ignores one of the sources of high costs.
The other is that our doctors are mostly either employed by the NHS, or employed by a private provider who is paid by the NHS ... yes, there are doctors who do private only work, but they are fairly small in number.
Perhaps our student loans system also helps - fees are £9k a year, but you start paying them back at 9% of income over £25k ... so it's essentially a graduate tax and they are fully written off after a set number of years if you don't pay them off.
A large component of healthcare cost in the US is simply healthcare use. We are deeply, deeply unhealthy with 75% overweight rates and absurd levels of pre/diabetes, which are the largest comorbidities of all, and comorbidities of each other. Costs will never be comparable until overweight/obesity rates and usage are comparable too. They are not.
High prices in the US are very unfortunately largely explained by usage, and no amount of profit-reducing or cost cutting will work unless you are cutting usage itself:
https://randomcriticalanalysis.com/2016/09/25/high-us-health...