The question for transformative nature is whether it merely supersedes or instead adds something new. E.G: Google translate was trained on books/documents translated by human translators and may in part displace that need, but adds new value in on-demand translation of arbitrary text - which the static works it was trained on did not provide.
> Substantiality of code does not apply to substantiality of style.
I'm not certain what you're saying here.
> The copying clearly is necessary for the purpose. No copying, no model.
Which, for the substantiality factor, works in favor of the model developers.
> It's the essence of an artist's look and feel that's being duplicated and used for commercial gain without a license.
Copyright protects works fixed in a tangible medium, not ideas in someone's head. It would protect a work's look/appearance (which can be an issue for AI when overfitting causes outputs that are substantially similar to a protected work), but not style or "an artist's look and feel".
If that were the case, no one would be able to paint any cubist paintings. (Picasso estate would own the copyright, to this day)
It's not that clear cut, there are a lot of nuances.
Substantiality of code does not apply to substantiality of style. What's being copied is look and feel, which is very much protected by copyright.
The copying clearly is necessary for the purpose. No copying, no model. The fact that the copying is then compressed after ingestion doesn't change the fact that it's necessary for the modelling process.
Last point - see first point.
IANAL, but if I was a lawyer I'd be referring back to look and feel cases. It's the essence of an artist's look and feel that's being duplicated and used for commercial gain without a license.
That's true whether it's one artist - which it can be, with added training - or thousands.
Essentially what MJ etc do is curate a library of looks and feels, and charge money for access.
It's a little more subtle than copying fixed objects, but the principle remains the same - original work is being copied and resold.