Power structures are bidirectional graphs. Examples, of this are college departments like Chinese Studies, South Asian Studies, European Studies, etc. These are methods of creating the history of the other and creating power over the other. I'm sure the Chinese, Europeans, Africans, etc. also have such histories.
Then you got further than I did! Someone should have dragged that guy to math class -- before you can prove two things are the same, you have to first define both of them, then make your case.
But if it wishes to use an existing word like "art" in a new sense, for instance to claim that all portrayal of humans is inherently pornographic, then IMHO it needs to be very careful to distinguish this from pre-existing meanings. The fact that some building on campus has "art" chiseled into the marble cannot be assumed to already imply agreement with some new meaning you invented 5 pages ago, a meaning which would have been very surprising to the guys who sponsored the building.
Even if you ultimately make a convincing case that the sense you describe is somehow more correct/useful/interesting than other ones, or encompasses them, you've got to act as if you haven't yet shown that. That's what I meant he should have learned in math class. And really the more honest course is to introduce new words for new concepts, not to try to muddle older ones, as Said successfully did.
But, to be fair, I didn't finish the book.
Like, wait right there.
One of the most valuable insights from scholarship like this is that we are all trapped in power structures. The "othering" that happens isn't the result of some demonic intention, it's just what people do. While Said takes great pains to make this point, most readers of the book that I've interacted with do not seem to grasp it. When I finished Orientalism I kind of chuckled because in many ways he engaged in the process that he was describing, "Occidentalizing" western area studies, as it were. I know it's not, but at some level I kind of hoped the book was a big meta-joke to illustrate the inescapability of the dynamic.