Yes, a good successful job can be done much cheaper - but, on the whole, the odds of success & quality degrade fast when less is spent. When it is YOUR life on the line, you may very well be willing to pay significantly more for those diminishing returns; they may be diminishing, but they are in fact greater returns. "Healthcare tourism" by Americans includes the ability to identify & access those pockets of excellence; those areas in general may not enjoy such inexpensive quality as the norm, nor have easy access to excellent outliers.
BTW: Americans (I speak as one) are a chronically dissatisfied bunch. Having remarkable access to excellence in all things, we bitch & moan about how it isn't oh so slightly better. Yeah we complain about the cost of healthcare, and at the same time demand the absolute very best, quick to sue the pants off any doctor whose work fails perfection standards by any statistically normal degree when something could have been done better regardless of extreme cost. I suggest caring little about opinion polls where objective statistics are available.
There is no evidence that this is the case. Note that the vast majority of the cost is due to the massive complexity of the system: every party involved - and there are many - wants their cut, and they don't necessarily contribute to the well-being of the patient or the efficiency of the process.
Last week, my dad (who is a doctor in Turkey) was telling me about a new study that compared the cost of healthcare services in various countries around the world and the satisfaction of patients. He said that the USA ranks close to the bottom of the index, meaning that considering how much American patients pay for healthcare, their level of satisfaction is incredibly low.
This is why "healthcare tourism" exists and is dominated by American patients.