I do think that Asia's top players are overall better than NA and EU as a whole. Dieminion talked about this when momochi showed a "beginner" tutorial to competitive usf4 with the wakeup OS
https://www.youtube.com/watch?v=W1VeqwFEmsg
But the gap isn't super large in a 2/3 setting. Its more obvious in a larger set like FT 5/7/10 such as the master series.
I don't think its character choice, but they do play a factor. I mean ryan hart plays yun and its not even close to kaz's level. Imo, its all due to the arcade scene and how arcades vs consoles are viewed.
Also I think it's how closely knit their community are. I'm not saying the American scene is selfish but there's like 4 huge regions in America (West, East, South, Midwest), 1 equivalent to japan in size. Information gets to more players there even with the day and age of internet. I mean that momochi OS, all of Japan knew about it and we barely discovered it even though it was online for like a year.