If China were to split into 10 countries each emitting 10% of what they do now it'd be the exact same emissions, but according to you it would be much better.
Similarly if the EU would become one country, that country would be high up on the list, much higher than member countries now! Oh no!
Looking at per capita emissions is much more fair.
Anyway, China's emissions are falling since last year ( https://www.carbonbrief.org/analysis-chinas-co2-emissions-ha... ). What's the US doing?
But policy is where real change needs to be made, and the effects of policy still scale with population in most cases.
Also, you don’t want all the low-population countries to each start contributing as much to global warming as the US.