I see a lot of people saying "community community community" as the reason why JP clear rates are so much higher than ours, but honestly, there's another reason at play that a lot of people aren't talking about.

If you raid in an MMO, and you play in NA/EU, you've probably already been raiding for over a decade, and you likely raid in another MMO, an MMO that isn't anywhere even near remotely as popular in Japan as it is in those two regions. Simply put, the "best" raiders in NA/EU are raiding in WoW.

JP doesn't have this issue, where FFXIV is the dominant MMO over there. As such, the playerbase that hits that content does tend to be higher quality on average, even though the top 1% is exactly the same.