Right, but in the weed analogy, the scale is used as a proxy to assume intent. When someone is caught with those 400 joints, the prosecution doesn't have to prove intent, because the law has that baked in already.

You could say the same in LLM training, that doing so at scale implies the intent to commit copyright infringement, whereas reading a single book does not. (I don't believe our current law would see it this way, but it wouldn't be inconsistent if it did, or if new law would be written to make it so.)