You're obviously not talking about energy policy or laws of physics. You're making moralistic judgements and anthropomorphizing a nation-state
If you wanna make comparisons (I don't, you do), per capita obviously matters. There's no reason why you should be holding members of one nation state to a stricter standard than members of another.
It's not the members of the nation state, it's the government. If one government is emitting more CO2 than any other, that government is the one that most needs to change policy because a policy change there is the place it would make the most difference.
Suppose there were only two countries in the world. One had 99.99% of the world's population and the other emitted twice as much CO2 per capita. Which one is most in need of changing if you want to make an impact on the problem?
If you wanna make comparisons (I don't, you do), per capita obviously matters. There's no reason why you should be holding members of one nation state to a stricter standard than members of another.