I don't disagree with your premise, but I'd argue that saying "there are no original ideas" in the context of a discussion of plagiarism is needlessly reductive. Even though I think I mostly agree with the author here, I think there are legitimate counterarguments that can be made; equating all of the ways someone can cite or build upon an idea with copying something word-for-word and claiming it's your own is not one of them though.

Sure they build upon them, you still need to add your 1% of original insight. There was a first person to realise that you could make fire by rubbing two sticks together.

Is my house a copy of the dirt it's on top of? Did the people who built my house build the dirt? There's a difference between "building upon" an idea and trying to claim you built the idea itself

No, I think I just find it reductive. The fact that some ideas are independently thought by multiple people does not feel like a compelling argument for normalizing copying someone else's work verbatim and trying to pass it off as your own.