I think what this misses is that the per-capita emissions matter too, not just overall emissions. It's kind of unrealistic to ask a country to lower its emissions when its per-capita emissions are already just a fraction of yours.

To give a more concrete analogy - suppose there are two countries, A and B. People in both countries like eating tuna. A has far fewer people than B, but the average person in A eats 10x more tuna than the average person in B. As tuna supplies dwindle, would it be reasonable for A to ask B to reduce their consumption of tuna?