There's been 1000's of cases just like this one, ever since "stocks" were a thing. Company execs misled shareholders about some *thing*, and those lies cost the stockholders a bunch of money.
In the end I'd guess it'll hinge mostly on whether or not it can be proven that the managers knew, or should have know, they were misleading investors. Discovery (emails and such) could be a real thorn for these execs
In the end, who wins will probably come down to whether Adobe execs said or signed of on statements that were categorically and unambiguously claiming the company "are not infringing on copyrights while training its AI". If they really did that, the plaintiffs I'm guessing will win, esp. since that site is well-known for pirated materials.
However if what they actually did was "characterizing the strategy as a generational opportunity to enhance productivity and creativity through responsible, commercially safe models natively integrated into its software ecosystem, it might be a tougher slog for plaintiffs. Because the key words here don't have hard definitions. They're weasel words and marketing-speak.
I don't know either way what the truth is (though I suspect the plaintiffs have 'em dead to rights), but that'll be the basic question.
Another interesting piece of this is that I would bet AI generally is playing havoc on Adobe's business model. "Why do I need Photoshop if I can just tell AI to conjure up the image I want" type of thing. So it may turn out legally difficult for shareholders to positively attribute the companies recent loss in value to their AI training scandal. That might not effect whether they win generally, but could have a large effect on how much they receive in recompense.
Another interesting twist would be if it turned out that the AI companies stole Adobe code to train their models to do what they do
I'll be watching with some interest, hope you'll keep us posted HPD, and keep their feet to the fire!