Japanese people are pretty bad.
1. They're so cheap
2. Their sportsmanship is literally -100
3. They ALWAYS leave after one if they win, as if they're better than you, without even giving you a chance to adapt to their dumb playstyles
4. They play (from my experience) very slowly, it gets boring in about 2 minutes when they play a Dedede who just jumps and b-airs
5. It's impossible to learn anything from them because they don't do anything different. No reads, nothing fancy, they just play soullessly, no passion whatsoever.
Seriously, when I was playing against anyone not Japanese, I noticed a huge difference. I never feel good when I win against a Japanese person and I don't feel bad when I lose because literally they're all the same garbage, roll spamming, projectile spamming, pretending like they're better even though they're bad, I mean, every other nationality has this, but after 9000 or so matches on FG, with 5000 american and 4000 Japanese, I can safely say that in my experience, they're the worst. I've become so cynical in the game because of the way Japanese people play.
I had to pick up Link because of all them, but they usually leave after one match so if you don't win, they automatically think they're better. So rematches are rare.
Also, another thing, this isn't related to nationality and whatnot, but I feel super disrespected when people don't bother to learn their character. If all you can do with Lucario is spam neutral and side b and try to use up-b offensively and not learn his comboes and stuff, and just ignore all the work Sakurai and the team did on him (Or any character, really) you're a piece of trash. Period. Characters like Link and Samus are so intricate, but people don't put the work in and put it all to good use. This is probably why people think Samus is so bad, because she's played horribly. Nobody innovates on their characters at all. If you love a character, you should put the effort in to make them look the best they can, instead of just spamming.