An objective hierarchy would make judging the value of art easier, but, like all else, nothing is ever that simple. You seem to be addressing the idea that there should be a universal application to the notion that art done in a specific way should be judged objectively higher or lower quality when compared to others of a different medium or source. Even if you could persuade everyone that such a hierarchy even exists, there would never be any universal agreement on what kind of boundaries should be set. "One man's trash is another man's treasure" is, indeed, an appropriate saying in this matter.
I think something to keep in mind is that A.I. art has some noteworthy factors working against it when it comes to the public's opinion about it. First, A.I. artwork has come under fire because of the behavior of the artists who use A.I. to create their art. There is a general fear of the proliferation of A.I. art supplanting more traditional forms of art both as display pieces and in commerce. We feel threatened that our own artwork will be ignored because loyal patrons find the works produced by an A.I. artist attractive enough to spend money on, an inherently unfair situation given the difference between the time and effort spent in production. A.I. artists are marketing the pieces they generate as if they were works produced by sweat, blood, and cramped muscles. At the same time, there appears to have been an intrusion in the professional industry due to stories of companies electing to use an A.I. to generate art as a cost-cutting measure.
Second, and, perhaps, more noteworthy, is the fact that A.I. art has dubious legal status. Whereas an artist who can sit and doodle on a sheet of paper until the art unfolds into a complete piece is unquestionably an artist with rights over their own work (and a cheater traces over their computer screen with a pen and scribbles the color too far outside the lines to be taken seriously), an A.I. is trained to mimic works found in a database of traditional artwork collected from perhaps something within the realm of hundreds of thousands of pieces and examples and thus has some questionable circumstances behind their output. When it was discovered that this database was constructed without the consent of the artists whose artwork was sampled, the logical reaction was outrage and attempts to protect artwork from being used as data to feed the programs. There still seems to be a question of whether A.I. art can be counted as legally permissible for sale as a copyrightable entity, permissible under the rules governing derivative works given that its construction is based on sampling others' art without any indication of creativity coming out of either program or user, or fraudulent as a work of plagiarism due to the lack of permission given by the artists who consider their work stolen.
Third is, of course, the fact that A.I. art requires little (if any) work from the user. This is perhaps the greatest of complaints in regard to the proliferation of A.I.-generated imagery. An A.I. uses prompts and keywords to generate any number of images is a short amount of time, while other artists have whole, hours-long or even days-long processes to churn out artwork of at least equal value. The user does not have to do much other than sit and judge which samples look worthy enough to post. When you compare A.I. usage to other forms of art production, even a kid rapidly drawing circles with a crayon expresses more physical effort. It is easy to equate poor artwork with a lack of effort, and I think such has been an easy judgement call to make given that, in traditional art, a lack of effort generally shows in the quality of artwork produced. If there is no effort, why should the art be considered art?
I think a fourth consideration should be the relative youth of A.I. art. Use of A.I. to generate art is still a very recent development, and all new things are always bound to have detractors hate it for simply being new. While I do not expect opinions to drastically change based on the passage of time, it is a persistent item in many modern innovations.
What it comes down to is that, at this point in time, it is hard to have any objective appraisal of A.I. artwork because far too many things are going on in the background with most of them steering the opinion of other artists and Internet users to a highly negative reaction by default. It is easier to carry this opinion because the above issues are a valid form of outrage which would greatly color a person's perception of A.I.-generated artwork. An objective hierarchy in artwork has already failed considering the foothold A.I. art has gained with some users who find such content about as desireable as non-A.I. art. I myself am willing to admit that I have occasionally found an A.I.-generated image visually appealing if only for being able to express a new concept. At the same time, my opinion of A.I. art tends to be low based on recurring visual flaws that ruin most images I have encountered. Even if we could factor out the news and events that have caused anger and derision, there would never be any sort of overriding objective observation that all people would agree on, and this goes with all art, not just A.I.-generated art.
