I edited my comment, since 70% tax rate is actually possible depending on the tax rate of the country you're living and whether they have a tax treaty with the US or not.
Where you get screwed is when countries have different philosophies on things. E.g. Canada doesn’t tax gains on your home, but you can’t write off mortgage interest on your taxes. Meanwhile USA taxes gains on your home but lets you deduct mortgage interest.
If you’re a dual citizen living in Canada, you pay both.
Or if you live in a country with predominantly sales taxes and no income taxes, well, now you get to pay lots of sales taxes and US income taxes.