My friends who work in animation describe a constant back and forth between the union and the studios over demands for more work for the same pay. Generative AI will just make it easier for directors to ask for even more ludicrous tasks.
And, in fact, this one of the reasons why VFX gets so heavily overused for stuff that you could do in-camera.
Is the actor wearing the wrong pants? Well, reshooting that requires paying union actors, gaffers, camera operators, etc. to shoot it again. Fixing it in post means you pay a couple of ununionized VFX artists.
It doesn’t happen with the actual costume department quite like that, but properly lit sets have definitely been widely replaced by expanses of greenscreen awash in nondescript lighting that hopes to vaguely match whatever the rendered surroundings turn out to be.
You could just assemble a cast, bring them into a greenscreen studio, and shoot a complete matrix of poses and angles and lighting variations. Then synthesize the film from that when someone decides what it should be about.
Some of the reason they gave for that at the time wasn't just saving on real world costume designers by outsourcing it to "cheap" VFX teams, but also for added "security" to avoid "spoilers" leaking to the press in tabloid photos.
(Spoilers of a sort: My favorite meta-joke on all this was Spider-Man: Far From Home's "primary" Mysterio costume which had tabloids and fans doing all sorts of speculation what the CG composited costume on top of it would look like, given the Avengers situation, only to find out that was actually the outfit for many of Mysterio's scenes because it very well fit the character in that medium.)
What are you basing this on and why would this be the case?