What do you mean by "output"?

If you compare emissions/export volume, then the US is behind lots of European countries, like Germany (or even Italy). Comparisons with the Netherlands (heavy agriculture) or Norway (big oil producer) are looking really bad, too: US is around 15 (tons CO2/capita/year), while China is at 8, Europe at 6ish and India at ~2.

The only countries I would classify as "surprisingly low" is France (at 4.5, thanks to massive past investments into electrification and nuclear energy) as well as India (at 2, mainly a result of low industrialization, and likely to rise sharply).

US + Canada is doing quite badly at CO2 emissions, even compared to wealthier nations like Luxembourg or Switzerland (!!). While part of it may be low population density, that is not the full story either (compare Norway).