I don't think it's possible to get away from that, we are both "plagiarizing" something else in a way just by writing these responses, because there are no new ideas, everything is a copy of something else, the only question is by how much, and can you tell. Obviously this goes down a philosophical rabbit hole... but I think the "reality" you describe is just as subjective as obviousness.
So, first, this is factually wrong, there are obviously new ideas, often rediscovered independently.
Second, seeing things in black and white is a fallacy. The amount obviously matters and what also matters is the _human_ work on top of the original work. LLMs are fundamentally different, human time (and work) has value, LLM time does not (it costs money to run but that is both different and inconsequential in comparison).
Third, you seem to forget that you can base academic work on that of other people, as long as you give proper credit. Just like are can base your code on that of other people, as long as you follow their code's license.
