Except that it's wrong: _revenue_ may be €8.4m per employee, but that's not the same thing as income. In a low-margin retail business like Amazon's, of course the revenues will be high, but almost all of that is compensated for by costs of revenue.
The only answer, is that it isn't actually as low margin as commonly stated and instead we have a tax system with loopholes that allow businesses to make a "profit" but by "reinvesting" in themselves they don't have to pay any taxes.