Defining "originality" and "authenticity" is quite straight forward. The first is concerned with the question of whether or not something is the origin of something or a reproduction or derivative of it or something else. While the latter is concerned with whether or not something is "real" or "genuine".
Now the much harder question is: What is art?
For example:
- Does it refer to things that are aesthetically pleasing?
- Is it defined by uniqueness and originality?
- Is it defined by (high) skill?
- Does it serve a purpose?
- Is it a goal in itself?
- Is it decoration or exploration?
- Ought it to be "authentic"/natural?
- Is fiction and imagination required for art?
- Does art require an artist?
- Does art require an observer?
- When art is what an artist makes, what makes one an artist?
- All of the above? None? Some? More than that? Less?
Like depending on the definition beautiful things for example can exist in nature independent of a (human) artist. Originality, skill and exploration might also be found in science, engineering and other crafts which are often not given credit for their creativity. Technically uniqueness can also be achieved without skill, though few people give that the appropriate credit and just because something is new doesn't mean people consider it a piece of art. Similarly if something serves a purpose it often seizes to be art, but something completely random is usually also seen as pointless.
So without raising a claim to completeness, I'd argue that:
Art is the original attempt of an individual of perfecting something.
So in that sense art does follow an aesthetic ideal of the artist that they try to achieve as best as they could, but that doesn't necessarily mean that it has to be "conventionally beautiful". Also often times aiming for perfection does require a certain amount of skill and effort. But idk if your ideal is just to broaden people's perspective of how we look at things, then also idk the black square which requires very little skill or even "fountain" which is just an ordinary pissoir bought off the shelf and which requires no skill at all, can serve that purpose. Though in that case the art isn't so much the object itself and its inception, but the context in which it is presented and the statement that the artist intends to make with it.
So doing the same thing sounds deceptively simple, but might actually be impossible. Like installing a light bulb and a mirror in Plato's cave is levels more elaborate and skillful than to just untie the prisoner, but it would still fall short of having the same revelatory effect.
So art usually isn't just about pleasing some aesthetic ideal of the masses, but rather seeks to go after a particular goal where no one else has gone before. Lots of art for example, is concerned with making emotions perceptible, finding the right notes, harmonies, words, rhythms, images and whatnot in order to create in the observer an effect similar to what you try to describe. Finding a language for which there are no words (yet).
So the problem with plagiarism isn't just that it takes away monetary value from the original artist. And yes you can have that discussion about whether or not something can be truly original in the first place. But even if it is a "perfect copy", it's possible that the change in context and intent of the statement just makes it inferior to the original as it lacks the non-object bound parts that have been replaced.
So idk, by now people probably already expect artists to be a bit off their rocker, but if a few hundred years ago someone deliberately decided to risk their income and reputation by wasting perfectly fine canvas in order to draw some butt-ugly nonsense, then people might have asked themselves "why"? And I'm not sure you get that same response for AI where it's essentially the definition of the algorithm that they aren't going for something in particular but just try to push the buttons that are statistically meant to be perceived by viewers as "positive".
So you're not thinking "what did the artist try to achieve with this", but rather "yea" or "nay". Because apart from tickling an undefined itch, there's no deeper meaning to be found. No intent, just statistics. And for the people interested in statistics it is interesting for other qualities than beauty.
Of course an "artist" could prompt the AI to generate art for them and thus trigger followup questions, but the problem is that unless they fine tune the result so much that it's a skill in and off itself, their "art" will just end up being mediocre and either confusing or just the aesthetic equivalent of "elevator noise" (nice inoffensive and forgettable the moment you step outside the door).
So "authenticity" in the art sense, might not just be about who's been doing it, but also about whether or not they have put some serious thought into it. Or whether they describe a real world observation and thus help out people in a similar situation to make heads or tails of it or whether they just imagined something like that and the reality is completely different from that imagination.
Also as said "originality" somewhat covers the societal problem of how to deal with artists, as that is either the best or worst job imaginable (and quite often is both, with high highs and low lows). As well as the problem that art doesn't just include the object or performance but also the conversation via context of the artist and the observer and especially the latter might be crucially missing with AI generated art even if they'd be capable of (re-producing) objects that are in some regard similar to what people like and learn to improve that.