The US isn't that vulnerable to the high debt-to-GDP ratio since the petrol dollar and dollar as the main currency for world trade, main in foreign reserves of many countries.
But the situation with Petrodollar is not the same as before. Many countries are dumping it. For example over the past couple of years two of the biggest energy exporters (Iran and Russia) have been using other currencies. One of the biggest oil importers (China) has been using CNY to pay, India is also starting to use Ruble, etc. to import energy. Another big oil exporter (Saudi Arabia) is also selling some of its oil in other currencies such as CNY.
In other words USD used to be global currency, it now mainly exists in Europe while it is slowly being abandoned in other regions.
I agree about the points you raised about China.