Your mixing up a lot of concepts around art into one thing. Aboriginal art has nothing really to do with generative AI art at the level that I'm talking about (aboriginals are human after all, and we're talking about the distinction between human art and non-human objects that are aesthetically appealing), but I will address your points.
> If artistic value is not one-sided and tied to the transformations in the observer's mind
Art is public and need no relation to transformations in the observer's mind. Art is a public concept in language related to human behavior, manifesting and reflecting certain human behaviors and abilities, like imagination.
> you get into situations where you invalidate the experiences of thousands of people because the "authentic human art" they were inspired by turns out to be a mechanical forgery
This is pretty unclear, we have the concept of forgery and it is not a new concept, just because something was beautiful and inspiring doesn't mean it's art (think a beautiful and inspiring coastline). If thousands of people fell prey to a forgery...so? A forgery is in relation to the real, so why not show them the actual existent work art, or simply explain about where it came from and see what they say? History is rife with people realizing they were lied to.
> or the aboriginal sculpture some archaeologist discovered, admired and wrote articles interpreting is discovered to be unworked stone.
Sculpture has a long tradition and is often understood as art by communicating that tradition. That's aboriginal sculpture, which is understood and put into context by present day members of that aboriginal culture or by people who have studied it. The flip side is things like "talismanic" objects, which have often been later put into context as unworked stone or completely different objects. That's simply archeology. Some artistic traditions are "lost", we only know of them through existing records. That's just history. Some may be lost in a more explicit sense in which they are unknown unknowns, but then that is just hypothesizing.
> Your position allows a dead person to have their experiences retroactively cheapened because of carbon dating and microstructural analysis. "How sad, it wasn't _really_ art though."
I don't know why you come to that conclusion. My point is pretty clear. Art is understood through the context of human agency. If we have the context and ability to place and recognize that in a work, then amongst other elements (for the purpose of aesthetics for instance), we generally refer to it as a work of art. There is a more casual way of saying such and such is "a work of art" --- but that way of saying it just means "aesthetically pleasing". There is a difference between the work of art that is a painting or a sculpture or a dance, and the "work of art" that is a beautiful landscape, and that is largely human agency and the use of imagination. So when you say:
> You can define art that way, but you end up with an immaterial, axiomatic essentialism that seems practically useful only to in drawing a circle and placing certain desirable artifacts inside and other indistinguishable artifacts outside.
You're ignoring my point: it's not about desirability, it's about insisting on the distinguishable characteristic of human agency which is not there in generative AI art. The study of art is largely about putting things into their context and, if anything, is extremely welcoming of non-traditional practices (think much conceptual art), but the through-line throughout is still human agency. That difference still persists whether we find generative AI art beautiful or not, it is still generative AI "art" and not human art with all that entails.