There is also a (IMO less likely, but still conceivable) scenario where weights ARE copyrightable, but represent fair use of the training data on grounds of being "sufficiently transformative".
I consider that one super likely, but then using the model to make competing works with one the artists in their own style is a non-fair use derivative work
Your case wouldn't be about style, it would be about specific elements that you posit were memorized and regurgitated by the model. The fact that you're creating art in the same style/medium as the author is what negates the "sufficiently transformative" fair use defense.
Basically, that world ignores the AI model completely. If your resulting work wouldn't be fair use if you directly were working with something from the training set, it wouldn't be fair use if you fed it through an AI model first.
