Only vs. China, Iran and Italy. We're within a factor of two (that is, about 5-6 days) of everyone else. A 5-6 day head start is not enough window to save ourselves with a travel ban.
And just like Italy went from "contained" to a country-wide lockdown in the space of a week, so will we at this point. Those tens of thousands of cases are incubating right now and will emerge in the coming days.
But it's also not the case when looking only at absolute numbers either. I would also argue that per capita is implied because it's the only way you can really make that comparison.
I’m not sure this is true, as the deaths from coronavirus are distinguishable based on their clinical features, as I understand it (e.g., the chest X-ray of a COVID-19 patient is readily identifiable)
In order to not significantly undercount the number of coronavirus deaths attributed to other causes in the US, there would need to be wide-spread testing here... which there isn't.
Imaging (by the way, you're referencing tests on live patients not dead ones) could be used as another kind of coronavirus test, though an extremely inefficient one, so probably is essentially un-used. Anyway, for pneumonia I believe we're talking about x-rays which is poor at distinguishing coronavirus (see link). Not to mention all of this is brand new. So approximately zero Radiologists are trained and using radiology in a clinical setting to diagnose coronavirus in people who have apparently died of pneumonia.