I don't know the current restrictions, but at least in the recent past, there were limitations on the number of foreign-born sumo wrestlers a stable could have. Despite that, the few Mongolians who are able to join a stable are dominating the sport. And I think a lot of sumo fans agree that their presence has been great for sumo. I have seen Hakuho wrestle on several occasions and feel lucky to have witnessed the greatest wrestler of all time. I can't imagine what the current sumo landscape would look like without the Mongolians who have given it so much fresh life. The article is a fascinating read.
> The most anticipated match of the July 2021 tournament pitted Yokozuna Hakuhō Shō against Ozeki (second rank) Terunofuji, who is also Mongolian. Having two foreigners competing in the oldest and most revered Japanese sport is similar to the final game of the baseball World Series being played between Mexico and Canada, while the Americans sit back and watch.
Nothing that uncommon to speak off. England is no longer a soccer giant, and the national composition of it's national team is well known.
South Asia completely steamrolls UK in cricket — a exquisitely British sport, so it was like a thunder out of the sky when Britishers finally got a cup in 2019 after many decades.
South America completely dominates Polo in a similar manner.
Soccer is a global sport, and cricket long ago became a part of South Asian identity. By contrast, sumo is played only in Japan (there is no Mongolian sumo league etc), to Japanese audiences, with Japanese sponsors.
Also, pet peeve (directed at the article, not you): sumo is the sport. The wrestlers are "sumo wrestlers", or "sumotori" if you insist on the original, but not "sumos".