I don't agree with your framing but let's accept it for the sake of this conversation.

The UK and Japan are not the only countries with more efficient healthcare systems than the US. We can look at a variety of countries, some of which have a higher GDP per capita than the US.

If we look at a graph of 'healthcare spending per capita' by 'GDP per capita' [1], we can see that the US is a massive outlier spending ~2x countries with comparable GDP per capita.

In fact, the US has a higher healthcare spending per capita than every other OECD country. By a large margin.

[1] https://www.healthsystemtracker.org/chart-collection/health-...