The rich will just go to whatever country happens to have the best person to treat the thing they need treating.

Had a colleague whose wife worked at a Swedish hospital and she had patients from all over the world, not because the Swedish health system or even that hospital was particularly fantastic, but because she was one of the top people in the world in this one very niche thing.

As the other commenter said, 'The rich will just go to whatever country happens to have the best person to treat the thing they need treating'.

Now, out of all developed countries, why did you mention Japan? IIRC, Japan produces little medical research compared to the UK or even Germany.

Japan isn't great about excellent expensive medical care outside of insurance.