Unless you can make a good argument that some humans have a natural or divine right to a bigger share of whatever total worldwide emissions budget we decide we can accept any kind of per country instead of per capita base allocation [1] make no sense.
This can be seen by considering what happens if countries split. A large country that is over their allocation in a per country system can simply split into two or more smaller countries, with the split designed so that each of the new countries has about an equal fraction of the former country's emissions.
This results in no change in the total worldwide emissions, but now that set of people that were before over their total allocation and high on the list of people that need to make big changes now are all in countries under their allocation and in the "should do something about it eventually but no need for big changes now" group of countries.
If they are clever about how they split the original large country into smaller countries they can immediately make free trade treaties and travel treaties between them that effectively make a common market with free travel like much of Europe now has so the split into multiple countries doesn't even change life much for the citizens of the new countries.
Whatever countries have now moved to the top of the "need big changes now" list because of this now have incentive to split, and so on.
[1] By base allocation I mean whatever share they would be allocated in a world with no trade. Actual allocations need to take into account people emitting more because they are making/growing things for other people which reduces the emissions directly attributable to those other people.