Specifically the US is already spending more federal tax dollars on healthcare, per capita, than the UK is spending on the NHS.
Now the NHS is underfunded but imagine what the US could afford in terms of healthcare quality and availability if you add what Americans are currently paying to their insurances on top of that.
And the inefficiencies aren’t just capitalist grift, btw: It’s also that the US system, systemically, does not do prevention. Lots of ER visits could be avoided if people wouldn’t have to fear bankruptcy when they go to a regular check-up, but noone gets turned down at the ER and noone can afford the bills so hospitals get stuck with the bills and the government has to bail them out. That’s where a huge chunk of that federal money is flowing, next to medicare and medicaid, which both cost way more than they should because aforementioned grift, and lobbyist-written laws enabling that grift.