On an aggregate level this is true and contrary to the prevailing sentiment of doomer skepticism, the developed world is usually still the best place to do it. On an individual level, a lot of things can go wrong between here and a million dollars.

  > make $1mm in a rich country and move to a poorer country and chill if you so desire

Fun fact what most people ignore: There have been around ~7000 people on Mount Everest - while the US alone has around 300.000 / 350.000 people earning more than 1 million USD a year.

So - its clear: Is more easier to become an "income-millionaire" than to climb Mount Everest! :-)