[0]: https://www.census.gov/library/publications/2023/demo/p60-28...
Cuba isn't poor because of an inefficient command economy. Cuba is poor because it has been denied access to its largest trading partner (and more) for over half a century. And people _still_ have a better healthy life expectancy in that country than in the US. Imagine what it could be like there if the US did more than pay lip service to world prosperity and peace.
"Host" nations agree to pay Cuba for the doctor's work, agree not to pay the doctor directly, and agree to deport them back to Cuba if they attempt to negotiate being paid directly. This is slavery by anyone's definition.