I'm gonna be real with you, Orientalism is way more "collonialist" than pointing out transmisogyny within Japanese culture
How many Japanese people do you talk to? I interact with them semi-regularly on Twitter, usually to try and find good TS works that scanlators haven't picked up yet.
There is a
genuine annoyance among the ones I know that western readers hyper-boil every single subgenre of their gender subversion down into "trans". Often ignoring the full spectrum of gender-nonconformity ranging from classic kabuki performances to modern day otokonoko (crossdressing/"femboi") mangas and so on. And what do you call it when you're pushing your narrative on their culture and art, against their comforts because you're the bigger more globally influential culture? That's colonialism, I'm sorry. I don't have a softer word for that mindset.
You can absolutely
enjoy their works from a trans lens. And I do think it's a good thing for you to do so and even evaluate it from that perspective! Critique and commentary is awesome! In fact, I'm sure it's incredibly helpful and enlightening to Japanese creators. Some have even said as much to me that many perspectives is important. But the point you cross the line is when you abandon the mindset of "I'm OK you're OK" for "I'm OK but you're objectively not OK".
Frankly, IMO it's
doubly important we come together instead of pushing each other apart. Japanese trans people -- like people considering or already on HRT -- absolutely do not feel safe right now. As you say, transmisogyny is no joke over there. And I said it before, but it's kind of amazing the standing law that mandated sterilization of people seeking HRT got repealed months after the Onimai anime busted all the charts. So whether or not Onimai passes your muster for sufficiently doing enough for trans people, I say that it's very possible it is. You're absolutely right that anime and manga
could be doing more. But I'd personally prefer not to let perfect be the enemy of the good. Even works not directly targetting an openly LGBT audience can and have done amazing good for the community. (rest in peace, Mr. Rogers)