Who do you think should hold the copyright on the model weights, the copyright holders of the individual works comprising the dataset or the ones who assembled the dataset?
They're a mathematical transformation of the source material.
As a trivial example, applying gray = .299 r + .587 g + .114 b to a pixel is also a mathematical transformation but it doesn't create a new copyright.
And thus, the model is a mathematical transformation and a derivative work of its source material.
However I am also of the opinion that the resulting model is sufficiently transformative and fills a different purpose than the source material and so the model is not infringing.
From the Perfect 10 case against Google and Amazon:
> …We conclude that the significantly transformative nature of Google's search engine, particularly in light of its public benefit, outweighs Google's superseding and commercial uses of the thumbnails in this case. … We are also mindful of the Supreme Court's direction that "the more transformative the new work, the less will be the significance of other factors, like commercialism, that may weigh against a finding of fair use."
That was dealing with thumbnails being used in search and it was found that thumbnails being used for search was sufficiently transformative and applied to a different purpose that Google's use didn't infringe.
I believe that a model is even more transformative given that bar.
That doesn't mean that the output of the model isn't infringing, but that's a human with agency creating and publishing that output which is a different artifact to be considered than the model weights.
Model weights are even less specific then that number, since they don't represent any specific source input at all.