There seems to be a huge contradiction between the 2 addressed issues.
1) balancing all 3 countries to about equal numbers (?)
2) requiring one country to conquer both of the other countries to win a war.
The Classic Ratio for attack is 3:1 and what any sane commander would wish for is 6:1. But now (or in near future) a country is expected to conquer and win with 1:2 odds?????
I think that either of these approaches could be good ALONE, but I have hard time seeing how they would work together. I actually give my ful support to concept 2. I think it alone could work as a balancing feature, since a large country would be fighting against 2 smaller countries... not like nowadays, when the 2 largest countries kill the smallest country.
The concept 1 also works against squadrons and small groups of friends, forcing them to split and/or communicate constantly where (in which arena and country) they could fly together.
PLEASE, go for concept 2... and reconsider forcing people to split their squadrons.