You're overlooking an important factor -- random distributions.
Unless there's a confounding factor that skews experienced players to one side, when you get above a few hundred enrolees there shouldnt be any meaningful difference between the countries' members - in quality, in personality, in years played, or even in eye color. That's what "random distribution" MEANS, and that's the basis for all the population based scientific studies you hear about on CNN or whatever.
That being so, let me ask you a question:
What's a more effective approximation of "equal sides" -- 40:10:10, or 20:20:20?
Neither will be completely even, due to their randomness, but which one is the BETTER GOAL?