I would agree that much more than we're usually ready to admit to ourselves is second-hand, but saying everything is going too far. Inventions and discoveries are happening all the time, at all scales.
Inventions and discoveries are basically a very advanced form of pattern recognition - seeing "interesting" regularities in some particular input where no-one has spotted them before.
And LLMs are capable of making discoveries in this sense, if you feed them data and ask to spot the regularities. They're not particularly good at it, but that's a different question from whether they're able to do it in principle.
Yes, in as far as LLMs can be said to make inventions and discoveries, this is clearly how they do it. And yes, these type of processes definitely play a big part in our human creative capacity. But to say this is all there is to it, is going too far in my opinion. We just don't know. There's still so much we don't understand about ourselves. We haven't designed ourselves after all, we just happened to "come to" one bright primeval day and since then we've been exploring and discovering ourselves. And again and again, we've found ourselves in that seductive spot where we thought we "got it" and there's nothing essential about ourselves we're still missing, only again and again to be proven wrong. Dogmas crumble, new dogmas coagulate, only to dissolve again. Or, we could use the more dignified word "paradigm".
I mean, to me at least, that is the definition of discovery. The exact process used to spot the pattern is an implementation detail.
And yes, I agree that we really just don't know too many things. But my impression is that we're overestimating just how complicated out behavior really is.
The rabbit hole goes very deep with these questions. For example, you left out above the other half of the equation: inventions. Our creative ability. Is that just more pattern recognition? And can discovery and invention be always cleanly teased apart? Also, what humans might have access to is something that is more simple than we imagine. Mystics and philosophers have tried to point towards it. One book that discusses these things in the context of western science and philosophy is Nature Likes to Hide: https://www.amazon.com/Nature-Loves-Hide-Quantum-Perspective...
I would argue that invention is the same thing, yes - identifying patterns in the environment that can be exploited for productive purposes.
FWIW I think it's not a coincidence that LSD - which kicks pattern matching capabilities of the brain into high gear, so to speak - is commonly used as a drug to boost both "creativity" and "inventiveness".