Indonesia has more players in double events. On the opposite, China has more players in single event. So counting number of players may not be truly representative. So I counted participation by events entered, meaning only counting double pair as one entry.
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Japan is getting close to China's level in the early 2010s where they can probably form 2 Uber Cup teams and it's not all that unlikely that those 2 teams will meet in the final. Already there for WD, not quite yet for WS.
If that day comes, wonder if anyone will start saying that their domination is unhealthy for the sport