I could imagine that if copyright law were to be extended in this way, artists would either be small enough to fall under the radar or select for popular enough artists that they could sub-license the 'copyrighted style' in question. Regardless, only large corporations and a select few 'superstar' artists would benefit at the expense of the vast majority of artists and the public.
If this were to pass (and I very much doubt there's a good chance of it happening), all is not lost because there is a wealth of public domain imagery that we can still train on. This could then snowball into providing richer datasets to train on.
I don't like the framing of a lot of these arguments. I'm paying taxes to provide a state apparatus that provides copyright legal protection for artists. I'm happy to do this, up to a point, as it's essentially a contract that provides incentives to innovation by rewarding artists, with the understanding that, eventually, the artists works get to be used by the public (that is, given to the public domain/commons).
Copyright law, at least in the US, specifically forbids ideas and "styles" to focus on specific realizations. I understand we're in a shifting landscape where technology is changing this narrative and that copyright law was created with different technology in mind but copyright law exists, presumably, as a compromise to incentivize artistic creation while serving the public good. Copyright law is not meant to be corporate welfare nor is it meant to protect the artist at the expense of the public, in perpetuity.
It would be nice to have a more reasoned argument instead of this knee-jerk reaction of theft.