I mentioned D&D books because of this post, but my statement was meant to apply to any RPG dealing with cultural or historical material:
There are still people who use oriental adventures in their 1E and 1E retroclone games. Like I mentioned before, I used 1E and 3E oriental adventures, greatly modified, to run 3rd edition wuxia-inspired campaigns (often taking classes here, mechanics there, reskinning them and using them for different kinds of martial heroes. The martial styles in both editions were useful as a foundation for what I was interested in doing. One of the big things OA introduced was Non-weapon proficiencies. So it is important in terms of the development of the game.
But there are also plenty of people who run the game straight as is, for a more pastiche setting.
I don't think it is a binary. Obviously anyone who has delved deeper into these topics, and has stayed with the hobby this long, is going to use newer games, be more aware of distinctions and information that OA didn't address or missed. But that doesn't mean you have to stop using OA. You can go back to it and run it sometimes (for a variety of reasons). Personally I sometimes like pastiche settings that are a bit gonzo. OA was basically like putting samurai movies, kung fu films and western inspired asian material (like Shogun or even the Karate Kid) in a blender. Now that isn't going to produce something terribly authentic. But it isn't meant to. It is just meant to be fun and to reflect the kind of media people found exciting at the time.
And clearly if you are trying to do something that is like historically based Tang Dynasty or genre specific (like wuxia) OA isn't really intended for that kind of focused flavor (though like I said, I found plenty of stuff to kitbash from both versions of OA). Before I was super into wuxia though, I was just interested in martial arts in general (doing both traditional and sport MA). And in those days, I found OA useful for running a D&D style campaign that had martial arts in it.
Random musings.
As a kid, I had my fair share of Ninja fascination. So I sympathize.
I became fascinated with Wuxia from the movie, Hidden Dragon Crouching Tiger.
Academically, I admire the I-Ching and its related philosophical Daoism, and know something about it. I was sad to be told that Daoism is increasingly extinct in China, and that one is more likely to come across it in the Chinese diaspora communities.
In my games, I havent built an East Asian region. If I were to do a historically-informed Ninja-esque character, I would use the Rogue class straightforwardly to build it. Probably the Assassin archetype. Make sure the gymnastic/stealth tropes are upto snuff. Unless I was actually in a Japan-esque setting, I would probably avoid the word "ninja". If I were to do a mythologically accurate ninja, I would do more research.
In highschool, a friend of mine is a Chinese American, who gamed with us. Interestingly, his background is from a Christian Chinese family. But, heh, he himself is a hardcore American (to the point of rebellion), and there was no chance of getting a Chinese-esque game from him.
@Dire Bare linked an article about how the fantasy setting of Avatar The Last Airbender, gets it right. Fire/Japan, Earth/China, Air/India, and Water/Inuit are prominent inworld identities. I admire all of these cultures for different reasons. It is cool that these nations appreciate Avatar. The point of the article is, the authors were intimate with the histories of these nations, thus the fantasy versions were more grounded and more realistic, and more authentic, while at the same time, allowing individuals to be unique individuals. I will keep this article in mind.
Now, you yourself are doing actual martial arts training, so you probably have some authentic exposure to reallife tradition. At the least, your games can probably talk about martial fighting styles with some intimacy and accuracy.
