'Common international parlance'?? Who are you speaking for? You only get to speak for you.
All of these are Americans. All of these nations are on the American continent.
yes, but no where are Argentinians or Mexicans referred to as Americans. If you can provide some examples where they are, go for it.
Europeans or Asians are cases where the continental location is used to describe the people of several countries. but even so, Germans are not Italians and Chinese are not Japanese.