Today's math question ... what are 4.2% and 18.8%

That is all

...but I don't believe the 18.8%.
I'm quite convinced there are highly populated countries that are GROSSLY underreporting cases & deaths.
I don't believe numbers out of Russia, China, India, or Brazil. That's almost 3.15 billion people.
That's doesn't excuse the terrible response here, but I think the % of deaths is much lower than 18.8%

True enough. But you work with what you have.

So ... if you just ignore the likely fiction from Russia, China, India, and Brazil you get a total death count of 1.25 million and a total population of 4.6 billion. And then ...

The US has 24.6% of the deaths and 7.1% of the population (of the slightly more believable countries).

And ... just for an extreme ... if for example, each of the lying countries really has 10 times their reported deaths, then the total count goes to 5 million dead with 7.8 billion people. and ...

The US has 6% of the deaths with 4% of the population.

Of course, in that exercise, I should probably also increase the deaths in the US by some TBD factor as well.

CDC & the insurance actuaries track unanticipated deaths. The best guess at this point is 20-25%.
So, while it's likely our death count is higher than reported, it's not a whole number multiple.
If we had a hard, accurate dataset, I would be unsurprised that the US is 8-10% of world deaths vs. 4% of world population.
Still disproportionate. Many, many of them avoidable.