I'm of the opinion that the eastern Europeans have an edge, but it may be more due to economic reasons or what seems to be less economic oppportunities = more choose careers in athletics.
The Germans generally rank high in the Olympic games and the World Cup (but lately there have been some foreigners in the mix).
The Finns have good long distance runners; South Slavs have good tennis and probably the best basketball players in Europe.
In MMA and boxing, the leaders tend to be Slavs, usually eastern European. But the Dutch also have great kickboxers.