Bedrockgames
I post in the voice of Christopher Walken
It's not that muddy, especially in this context.
From the back cover of the original OA:
The mysterious and exotic Orient, land of spices and warlords, has at last opened her gates to the West.
There is then some more text, more prosaic, that concludes "The world of samurai and ninja awaits!" This already implies that I can't build a samurai using a D&D fighter, or a ninja using a D&D thief, assassin or monk. But why not?
Nothing is stopping you from building a samurai with a D&D fighter, but Samurai, Ninja and Wuxia tropes are a bit different from King Arthur tropes, so having a class that reflects the genres these come from is good in my opinion. I don't think it is a commentary on differences between western and asian cultures, so much as it is an effort to emulate and celebrate the media these things come from. I am not saying OA perfectly captures these or that they couldnt' be improved upon. But I don' think 'the world of samurai and ninja' is a huge problem