I don't think the best fighters/trainers are in the US, but I still agree with TS, because:
1. If you want to fight in an American org, it will be a huge disadvantage with the jetlag if you travel from Asia or Europe. 6-7 weeks is just not enough time to be acclimatised.
2. In part, the US have a strong tradition for wrestling. Yes, many other countries do to, but not all.
3. Many substances and "sports-drinks" are allowed in the US, but not in Europe. This 9is an advantage in most sports.
4. The big camps have equipment and experience to do testing, and know more about the USADA, and will find ways to get around it. In other parts of the world, it is like being blindfolded, and never knowing when they will show up or if nthe stuff is out of the system.
On the other hand, it is a bit strange that we have had so many great europen/asian/south-amaerican champions and top ten fighters in a US league, where you should think at least all top ten should be from the US.