What's more likely:

A) 90% of non-Japanese players (in the ENTIRE WORLD) just happen to not follow the directions and miraculously 80% the winners were Japanese because of this

Or

B) The devs are biased towards Japanese player's ideas/culture and consciously or sub-consciously picked Japanese winners.

Unless Japanese players make up 80% of the playerbase, then no, it's not cool, and it is insulting, and not conspiratorial.

Also, most of the winning styles are just so..safe.