Is the decentralization ruined if someone has outcompeted computer hash power than others?
This is another very popular question.
There are two kind of decentralized fairness: fairness of result and fairness of process. For the first one, the fairness comes from absolute fair distributed of the computer power of each country. However for the second one, everyone has the same opportunity to compete the computer power by investing money and resources.
Obviously, priority of results or process is conflict to each other. You can only choose either one of them. Bitcoin chooses the fairness of process. It doesn’t matter the result. What it matters is that even one of those three countries controlled the major hash powers, can any other one join the competition freely or not. If the competition is still open for everyone, then it is still decentralized.
Also, even for the result of some "centralization" won't destroy "decentralization" of bitcoin as the major hash power owner has no incentive to do bad things. For this part of the argument, please refer to my another article to discuss about hackers and motivations: